Construction of a tantalum nitride film on a semiconductor wafer

ABSTRACT

The construction of a film on a wafer, which is placed in a processing chamber, may be carried out through the following steps. A layer (film) of tantalum nitride material is deposited on the wafer. Next, the layer of tantalum nitride material is annealed. The deposition and annealing may both be accomplished in the same chamber, without need for removing the wafer from the chamber until both steps are completed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of the following U.S. PatentApplications:

U.S. patent application Ser. No. 08/498,990, now abandoned, entitledBIASED PLASMA ANNEALING OF THIN FILMS and filed on Jul. 6 1995;

U.S. patent application Ser. No. 08/567,461, now abandoned, entitledPLASMA ANNEALING OF THIN FILMS and filed on Dec. 5, 1995;

U.S. patent application Ser. No. 08/677,185, entitled CHAMBER FORCONSTRUCTING AN OXIDIZED FILM ON A SEMICONDUCTOR WAFER and filed on Jul.9, 1996;

U.S. patent application Ser. No. 08/677,218, now abandoned, entitledIN-SITU CONSTRUCTION OF AN OXIDIZED FILM ON A SEMICONDUCTOR WAFER andfiled on Jul. 9, 1996;

U.S. patent application Ser. No. 08/680,913, now abandoned, entitledPLASMA BOMBARDING OF THIN FILMS and filed on Jul. 12, 1996;

U.S. patent application Ser. No. 08/810,221, entitled CONSTRUCTION OF AFILM ON A SEMICONDUCTOR WAFER and filed on Feb. 28, 1997; and

U.S. patent application Ser. No. 08/808,246, entitled CHAMBER FORCONSTRUCTING A FILM ON A SEMICONDUCTOR WAFER and filed on Feb. 28, 1997.

Each of the aforementioned related patent applications is acontinuation-in-part of U.S. patent application Ser. No. 08/339,521,entitled IMPROVED TITANIUM NITRIDE LAYERS DEPOSITED BY CHEMICAL VAPORDEPOSITION AND METHOD OF MAKING and filed on Nov. 14, 1994, nowabandoned. Each of the aforementioned related patent applications ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention is directed toward the field of manufacturingintegrated circuits.

B. Description of the Related Art

When manufacturing integrated circuits, deposition processes areemployed to deposit thin layers of insulative material and conductivematerial onto wafers. Deposition has been performed through various wellknown processes, such as chemical vapor deposition ("CVD") and physicalvapor deposition ("PVD" or "sputtering").

In a CVD process, a wafer is loaded into a chemical vapor depositionchamber. Conventional CVD processes supply reactive gases to the wafersurface where heat-induced chemical reactions take place to form a thinfilm layer over the surface of the wafer being processed. One particularCVD application is the deposition of a titanium containing compound,such as titanium nitride, over a wafer from a process gas that includesa metallo-organic compound. One such compound is tetrakis (dialkylamido)titanium (Ti(NR₂)₄) having the following structural formula: ##STR1##wherein R at each occurrence independently is in an alkyl group, of, forexample, 1-5 carbon atoms. For example, it is common to usetetrakis(dimethylamido) titanium (TDMAT), which has the formulaTi(N(CH₃)₂)₄.

A carrier gas, such as helium, argon, nitrogen, or hydrogen brings thecompound into the chamber, so that it may be infused with energy. Theenergy may be generated through a thermal heat source, in the case ofthermal CVD, or a radio frequency ("rf") signal source, in the case ofplasma enhanced CVD. The energized chemical vapor reacts with thewafer's surface to form a thin layer of material on the wafer. When theTDMAT chemical vapor is used, a titanium nitride film is deposited onthe wafer's surface.

In a sputtering process, a wafer is placed in a physical vapordeposition ("PVD") chamber, and the chamber is filled with a gas, suchas argon. A plasma containing positively charged ions is generated fromthe gas, by creating an electrical field in the chamber. The positivelycharged ions accelerate and collide into a target material, which ismounted in the chamber. Atoms of the target material are therebyseparated from the target and deposited on the wafer to form a layer oftarget material on the surface of the wafer.

In a traditional sputtering process, the bombardment of the targetmaterial by the positively charged ions is enhanced by providing anegative bias to the target material. This is achieved by providing aradio frequency signal to an electrode that supports the targetmaterial.

A separate rf signal may be inductively coupled to the chamber forgenerating positively charged ions in a high density plasma PVD chamber.A high density plasma PVD chamber may include another rf signal coupledto a wafer support for improving the attraction of the target materialto the wafer.

A deposition chamber, such as a CVD chamber or a PVD chamber, may beused to deposit diffusion barriers in an integrated circuit. Diffusionbarriers inhibit the diffusion of a contact metal, such as aluminum andcopper, into the active region of a semiconductor device that is builton a silicon substrate. This prevents the interdiffusion of a contactmetal into the substrate. Unlike an insulative layer of material, adiffusion barrier forms a conductive path through which current mayflow. For example, a diffusion barrier may be employed to overlie asilicon substrate at the base of a contact hole.

A severe interdiffusion between a contact metal and a silicon substratecan begin to take place when the integrated circuit is heated totemperatures in excess of 450° C. If an interdiffusion is allowed tooccur, the contact metal penetrates into the silicon substrate. Thiscauses an open contact in the integrated circuit and renders theintegrated circuit defective.

In the fabrication of integrated circuits, there has been an increaseduse of aluminum and copper metallization processes operating at hightemperatures, in excess of 450° C. Therefore, it desirable to havediffusion barriers with a greater ability to inhibit the diffusion ofcontact metals, such as aluminum and copper.

Traditionally, diffusion barriers have been made thicker to accommodatesuch a desire. However, smaller geometries are being employed in thefabrication of integrated circuits. The smaller geometries decrease thedimensions of contact holes, thereby making it desirable for diffusionbarriers to become thinner and more conformal.

FIG. 1 illustrates a diffusion barrier 100 that resides between aconductive region 105 of a silicon substrate 101 and a contact plug 102.A contact hole 103 is formed in an insulative layer of material 104,such as silicon dioxide, which overlies the substrate 101. The diffusionbarrier 100 is ideally formed so that it is thin and substantiallyconforms to the contours of the surface of the contact hole 103.

If the diffusion barrier 100 is thin and highly conformal, the contactmetal 102 is able to form a sufficiently conductive ohmic contact withthe silicon substrate's conductive region 105. If the diffusion barrier100 is too thick or poorly formed, as shown in FIG. 2, it will preventthe contact metal 102 from forming a sufficiently conductive ohmiccontact with the substrate region 105.

In FIG. 2, the poorly formed diffusion barrier 100 severely narrows theopening of the contact hole 103. The narrow opening causes the contactmetal 102 to form so that it does not reach the base of the contact hole103. As a result, a void 106 is formed.

In order to ensure a good ohmic contact between the contact metal 102and the substrate region 105, it is desirable for the resistance of thediffusion barrier 100 to be minimal. Typically, a resistivity value of1,000 Ω-cm or less is acceptable. One material that has beensuccessfully employed as a diffusion barrier is titanium nitride (TiN).

However, some deposition processes, such as those using TDMAT, providean unstable barrier layer having high resistivity. In the case of TDMAT,this is partly due to a significant fraction of the deposited barriermaterial being composed of a carbon (hydrocarbons, carbides, etc.).Further, the titanium, a chemically reactive metal, may not becompletely reacted in the film. It would be desirable to treat such alayer of barrier material with a post-deposition processing, so that itsresistivity is reduced and stabilized.

In manufacturing an integrated circuit, it is desirable to performsuccessive steps of the manufacturing process, such as deposition andpost-deposition processing, in the same chamber ("in-situ"). In-situoperations reduce the amount of contamination that a wafer is exposed toby decreasing the number of times that the wafer is required to betransferred between different pieces of manufacturing equipment. In-situoperations also lead to a reduction in the number of expensive pieces ofmanufacturing equipment that an integrated circuit manufacturer mustpurchase and maintain.

Accordingly, it would be desirable to construct a highly conformal thindiffusion barrier with an increased ability to inhibit the diffusion ofcontact metals, such as aluminum or copper. Additionally, it isdesirable for such a diffusion barrier to have a resistance that allowsthe diffusion barrier to form a good path for current flow. It wouldalso be desirable to construct such a diffusion barrier in-situ.

SUMMARY OF THE INVENTION

An apparatus and method in accordance with the present inventionprovides for carrying out the in-situ construction of a highly conformaldiffusion barrier with improved resistivity. By practicing aspects ofthe present invention, the diffusion barrier's ability to impede thediffusion of contact metals, such as aluminum or copper, may beenhanced. Such an enhancement of the diffusion barrier will notsignificantly enlarge its thickness or resistivity beyond acceptablelimits.

A semiconductor processing apparatus, which enables practicingembodiments of the present invention, may include a processing chamber,showerhead, wafer support, and rf signal means. In one embodiment of thepresent invention, the semiconductor wafer processing apparatus iscapable of performing chemical vapor deposition.

The showerhead is adapted to supply gases in the processing chamber. Thewafer support provides for supporting a wafer in the processing chamber.The rf signal means may be coupled to both the showerhead and the wafersupport for providing a first rf signal to the showerhead and a secondrf signal to the wafer support. Alternatively, the rf signal means mayonly be coupled to provide a rf signal to the wafer support.

The wafer support is supported in the processing chamber by a supportarm. The support arm couples the rf signal means to the wafer support.The support arm also couples a thermocouple housed in the wafer supportto a temperature determination device for measuring the temperature ofthe wafer support. The thermocouple is electrically isolated from the rfsignal means.

When practicing an aspect of the present invention, a film may beconstructed on a wafer. First, a layer of material is deposited on thewafer. The material may be a binary metal nitride M_(x) N_(y) or aternary metal silicon nitride M_(x),Si_(y) N_(z) (where M may betitanium Ti, Zirconium Zr, hafnium Hf, tantalum Ta, Molybdenum Mo,Tungsten W, and other metals). The deposition of the material may becarried out by a variety of means, such as chemical vapor deposition andphysical vapor deposition.

After the material is deposited, the material is plasma annealed, so asto reduce the resistivity of the layer of material. The plasma annealingmay include an exposure of the material to an environment containingions and electrically biasing the layer of the material to cause theions to impact the material.

Alternatively, the annealing may consist of multiple annealing stepsthat are performed sequentially with different gases. For example, afirst annealing step may employ a mixture of nitrogen and hydrogen,while a subsequent annealing step uses a mixture of nitrogen and helium.The subsequent annealing step removes hydrogen molecules from thematerial to reduce its resistivity.

Once the annealing is completed, the layer of material may be oxidized.The oxidation enhances the material's ability to inhibit the diffusionof contact metals, such as aluminum. Alternatively, the annealed layerof material may be exposed to a silane gas to enhance the material'sability to inhibit the diffusion of contact metals, such as copper.

In accordance with the present invention, the deposition, annealing, andeither oxidation or silane exposure may all be performed in a singlechamber, without need for removing the wafer from the chamber before allthree operations are completed. Accordingly, the deposition, annealingand either oxidation or silane exposure of the material may be performedin-situ.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the present invention are explained with the help ofthe attached drawings in which:

FIG. 1 illustrates a contact plug in an integrated circuit, whichincludes a diffusion barrier.

FIG. 2 illustrates a contact hole in an integrated circuit that isobstructed by a diffusion barrier.

FIG. 3(a) illustrates a chemical vapor deposition chamber.

FIG. 3(b) illustrates a wafer support and support arm for the chambershown in FIG. 3(a).

FIG. 4 illustrates a multichamber processing apparatus.

FIG. 5 illustrates one embodiment of a wafer processing chamber inaccordance with the present invention.

FIG. 6 illustrates a longitudinal cross-section through the wafersupport and support arm shown in FIG. 5.

FIG. 7 illustrates an enlarged cross-section of the support arm shown inFIG. 6 at the point where the support arm supports the wafer support.

FIG. 8 illustrates a partial cross-section along lines 6--6 in FIG. 7.

FIG. 9(a) illustrates a top view of the support arm shown in FIG. 6.

FIG. 9(b) illustrates a longitudinal cross-section along line 7--7 inFIG. 9(a).

FIG. 10(a) illustrates a plan view of a thermocouple isolator in thesupport arm shown in FIG. 6.

FIG. 10(b) illustrates a longitudinal section along line 8--8 in FIG.10(a).

FIG. 11(a) illustrates a plan view of a rf power strip isolator in thesupport arm shown in FIG. 6.

FIG. 11(b) illustrates a partially sectioned elevation of the isolatorshown in FIG. 11(a).

FIG. 12 illustrates a plan view of an underside retaining plate of thesupport arm shown in FIG. 6.

FIG. 13 illustrates a cross-section showing details on the fixed end ofthe support arm shown in FIG. 6.

FIG. 14 illustrates connector details of the rf power strip located inthe support arm shown in FIG. 6.

FIGS. 15(a)-15(c) illustrate embodiments of the matching network that isshown in FIG. 5.

FIG. 16 illustrates an alternate embodiment of a semiconductor waferprocessing chamber in accordance with the present invention.

FIG. 17 illustrates an alternate embodiment of a semiconductor waferprocessing chamber in accordance with the present invention.

FIG. 18 illustrates a graph of sheet resistance versus time for titaniumnitride film deposited by using a conventional deposition process.

FIG. 19 illustrates a Rutherford backscattering spectrum of a titaniumnitride film deposited on a silicon wafer using a conventionaldeposition process.

FIG. 20 illustrates Table I.

FIG. 21 illustrates Table II.

FIG. 22 illustrates Table III.

FIG. 23 illustrates a Rutherford backscattering spectrum of a titaniumnitride film deposited using chemical vapor deposition with a gas flowof NF₃.

FIG. 24 illustrates an Auger sputter analysis graph of a titaniumnitride film in accordance with the present invention.

FIG. 25 illustrates Table IV.

FIG. 26 illustrates an Auger surface spectrum of elements of anothertitanium nitride film in accordance with the present invention.

FIG. 27 illustrates a graph of the atomic concentration of variouselements in the titanium nitride film of FIG. 26.

FIG. 28 illustrates an Auger surface spectrum of elements of a Controltitanium nitride film.

FIG. 29 illustrates a graph of the atomic concentration of variouselements in the Control titanium nitride film of FIG. 28.

FIG. 30 illustrates an Auger surface spectrum of elements of anothertitanium nitride film in accordance with the present invention.

FIG. 31 illustrates a graph of the atomic concentration of variouselements in the titanium nitride film of FIG. 30.

FIG. 32 illustrates Table V.

FIG. 33 illustrates the absorption of oxygen by films produced inaccordance with the present invention.

FIGS. 34(a)-34(c) illustrate the reduction of organic carbon content offilms produced in accordance with the invention.

FIGS. 35(a)-35(b) illustrate the improved film resistance in vias andsalicide contacts formed in accordance with the present invention.

FIG. 36 illustrates the resistivities of films produced using differentnumbers of cycles of deposition and plasma treatment.

FIG. 37 illustrates a plot of film resistivity and bias voltage as afunction of plasma process pressure.

FIG. 38(a) illustrates the effects of annealing duration and frequencyon film resistivity.

FIG. 38(b) illustrates a further example of the effects of annealingduration on film resistivity.

FIGS. 39(a)-39(b) illustrate Auger electron spectroscopic depth profilesfor titanium nitride films formed by successively depositing andannealing layers of titanium nitride.

FIG. 40 illustrates an x-ray diffraction glancing angle scan of a 1,000Å titanium nitride layer deposited on a silicon wafer using conventionalchemical vapor deposition.

FIG. 41 is an x-ray diffraction glancing angle scan of a 1,000 Åtitanium nitride layer deposited on a silicon wafer and annealed inaccordance with the present invention.

FIG. 42 illustrates Table VI.

FIGS. 43(a)-43(b) illustrate the chemical composition of non-oxidizedand oxidized diffusion barriers, respectively, that are formed inaccordance with one embodiment of the present invention.

FIG. 44 illustrates the resistance characteristics of diffusion barriersthat are formed in accordance with one embodiment of the presentinvention.

FIG. 45 illustrates an Auger depth profiling of a film formed usingsilicon stuffing in accordance with the present invention.

FIG. 46 illustrates an Auger depth profiling of a film formed bydeposition of a material containing silicon in accordance with thepresent invention.

FIG. 47 illustrates a comparison of the resistivity and composition ofthe films shown in FIG. 45 and FIG. 46.

FIG. 48 illustrates a control unit for controlling a chamber that isused for constructing a film on a substrate in accordance with thepresent invention

FIG. 49 illustrates a sequence of operations performed by the controlunit in FIG. 48 in one embodiment of the present invention.

FIG. 50 illustrates a sequence of operations performed by the controlunit in FIG. 48 in an alternate embodiment of the present invention.

FIG. 51 illustrates a Rutherford backscattering spectrum of a tantalumnitride film deposited on a silicon wafer prior to and after annealingin accordance with the present invention.

FIG. 52 illustrates Auger electron spectroscopic depth profile fortantalum nitride film prior to annealing in accordance with the presentinvention.

FIG. 53 illustrate Auger electron spectroscopic depth profile fortantalum nitride film formed by successively depositing and annealinglayers of tantalum nitride in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A. Chambers forProcessing Wafers

1. Overview

FIGS. 3(a) and 3(b) jointly depict a traditional CVD chamber 10. The CVDchamber 10 includes a processing chamber 12 in which a wafer 14 issupported by a wafer support 16, such as a susceptor. The wafer support16 is supported by a circular disk 18, which is typically made of amaterial such as alumina ceramic. The disk 18 rests on the free end 20of a support arm 22. The support arm 22 defines a cantilever with itsfixed end 24 mounted to a stem 26. The stem 26 is capable of verticaldisplacement under action of a displacement mechanism 28. Thedisplacement mechanism 28 operates to move the support arm 20 verticallywithin the processing chamber 12.

During the processing of a wafer 14, gas is injected into the processingchamber 12, via a showerhead 36. The showerhead 36 is typically mounteddirectly above the wafer 14.

In operation, the interior of the processing chamber 12 is heated by aset of infrared lamps 30 mounted beneath the CVD chamber 10. The lamps30 irradiate the interior of the processing chamber 12 through a quartzwindow 32, which is located between the lamps 30 and the interior of theprocessing chamber 12. The lamps 30 serve to heat both the interior ofthe processing chamber 12 and the wafer support 16. As a result, a wafer14 on the wafer support 16 is also heated.

To enhance the heating of the wafer support 16, the ceramic supportingplate 18, as shown in FIG. 3b, includes a number of holes 34 formedtherethrough. The typical arrangement of holes 34 shown in FIG. 3b makesit apparent why the plate 18 is often referred to as a "Swiss Cheese"plate.

Thermal CVD wafer processing is very sensitive to the wafer temperature.To ensure that the wafer remains at an appropriate temperature, thetemperature of the wafer support 16 is measured by a thermocouple 38.The thermocouple 38 is supported at the free end 20 of the support arm22 and mounted within the body of the wafer support 16. An electricallyconductive cable 42 couples the thermocouple to a temperaturedetermination device 40, which is mounted outside the processing chamber12. The cable 42 typically runs along a bore formed centrally within thesupport arm 22.

FIG. 4 depicts a multichamber vacuum system, which is suitable forcarrying out the manufacture of a wafer including integrated circuits.Chamber A will provide for the pre-cleaning of a substrate upon whichthe integrated circuits are to be formed. After pre-cleaning, thesubstrate is transferred to a CVD chamber B, so that a film may bedeposited onto the substrate. The substrate will then be transferred toa post-deposition treatment chamber C for improving the quality of thedeposited film.

If it is desirable to "stuff" the film with a substance that enhancesthe film's operation as a diffusion barrier, the substrate may betransferred to chamber D in which such "stuffing" may be performed. Forexample, the film may be a layer of titanium nitride material, which isto be stuffed with oxygen to reduce the diffusivity of the film foraluminum. The stuffing of a titanium nitride barrier layer with oxygenis disclosed in U.S. Pat. No. 5,378,660, entitled BARRIER LAYERS ANDALUMINUM CONTACTS and issued to Ngan, et al.

Either of the above described systems may be employed for practicingaspects of the present invention. However, neither system provides theability to deposit a material on a wafer and perform post depositionprocessing on the material to form a film within a single chamber. Suchpost deposition processing may include annealing, oxidizing, exposure tosilicon, or a combination thereof.

2. A Chamber for In-situ Operations

FIG. 5 illustrates a semiconductor wafer processing chamber 110A inaccordance with the present invention. The wafer processing chamber 110Aprovides for performing a series of in-situ deposition andpost-deposition processing steps on a semiconductor wafer 114. Inaccordance with the present invention, the chamber 110A depicted in FIG.5 may be a chemical vapor deposition chamber as is described in detailin U.S. patent application Ser. Nos. 08/567,461 and 08/677,185.

Wafer processing chamber 110A eliminates the need for employing multiplechambers to deposit and treat a material in accordance with the presentinvention. For instance, the wafer processing chamber 110A may beemployed to form a film on a wafer by depositing a material on the waferand annealing the deposited material to stabilize and reduce itsresistance. As a result, the wafer will not be exposed to damagingimpurities that are outside of the chamber 110A during the formation ofthe film.

As shown in FIG. 5, the semiconductor wafer processing chamber 110Aincludes a processing chamber 112, which is coupled to ground. Asemiconductor wafer 114 may be supported in the processing chamber 112on a wafer support 116, which may be the same as the wafer support 16shown in FIGS. 3(a) and 3(b). The wafer support 116 may be a susceptor,a pedestal, a resistive heater, or any other suitable means forsupporting the wafer 114.

In FIG. 5, the wafer support 116 is a susceptor, which is the type ofwafer support that is often used when lamps are employed to irradiatethe wafer support 116. The susceptor is made of anodized aluminum and issupported by a conventional alumina ceramic support plate 118, which issimilar to the support plate 18 in FIG. 3b.

The combination of the support plate 118, wafer support 116 and wafer114 is supported on a free end 120 of a cantilevered alumina support arm122. A fixed end 124 of the support arm 122 is mounted to a generallyvertically moveable stem 126, which is electrically isolated from theprocessing chamber by isolator 160. The vertically moveable stem 126 isvertically displaceable under the action of a displacement mechanism128.

The processing chamber 112 and its contents are heated by means ofconventional lamps 130, which irradiate the wafer support 116 through aconventional quartz window 132. The semiconductor wafer processingchamber 110A further includes a temperature determination device 140.The temperature determination device 140 is coupled to the wafer support116 to sense the temperature of the wafer support 116. A vacuum pump,pressure gauge and pressure regulator valve are all included in apressure control unit 157. The pressure control unit 157 adjusts thepressure in the processing chamber 112 and exhausts both carrier gasesand reaction by-products from the processing chamber 112.

A showerhead 136 is placed above the wafer support 116 in the processingchamber 112 and is electrically isolated from the chamber 112 by meansof isolator 159. The showerhead 136 is supplied with processing gasesfrom a gas panel 52. The gas panel 52 is controlled by a gas panelcontroller 50 in the form of a computer.

In order to perform post-deposition annealing, the semiconductor waferprocessing chamber 110A includes a rf source 142. The rf source 142applies rf power to the showerhead 136, which operates as a firstelectrode, and the wafer support 116, which operates as a secondelectrode. The rf source 142 may be capable of providing signals withfrequencies less than 1 MHz, and preferably providing signals with afrequency of 350 KHz. Providing rf signals to the two electrodes 136 and116 overcomes challenges that are not present in providing rf signals totwo electrodes in other traditional semiconductor wafer processingchambers, such as a PVD chamber.

In embodiments of the present invention, it is possible to prevent theapplication of excessive negative bias to the showerhead 136. Excessivenegative bias on the showerhead 136 can cause increased ion bombardmentof the showerhead 136 which results in the generation of contaminantparticles.

It is desirable to have a great deal of ion bombardment of a targetelectrode in a traditional PVD chamber. In a traditional PVD chamber, atarget electrode supports a target of material to be deposited. Thetarget electrode is given significant negative bias, so that ionsreadily collide with the target material to provide for deposition ofthe target material.

Further, the negative biasing of a wafer support and the control ofwafer temperature in a traditional sputtering process are typically notcritical. This is not true in embodiments of the present invention.Controlling negative bias on the wafer support 116 is desirable forestablishing an optimum level of ion flux towards the wafer 114.Accurately setting the temperature of the wafer 114 is desirable forperforming both deposition and post-deposition processing of depositedmaterial.

Accordingly, the wafer support 116 provides the dual function of beingcoupled to an rf source 142 and housing a thermocouple temperaturesensing mechanism (not shown). The rf source 142 provides forcontrolling the negative biasing of the wafer support 116, and thethermocouple provides for monitoring the temperature of the wafer 114.

The wafer support 116 and support arm 122 are designed to isolate the rfsource signals from the thermocouple signals, so that accurate wafertemperature readings may be made. This isolation enables both the rfsource signals and thermocouple signals to be accurately transferredwithin the chamber 110A, so that the wafer 114 is both biased and heatedproperly. The details of the wafer support arm 122 are described belowwith reference to FIGS. 6-14.

3. The Wafer Support Arm

Referring generally to FIGS. 6-9(b), wafer 114 is supported on the wafersupport 116 which is itself supported by a conventional "Swiss Cheese"alumina ceramic support plate 118. A thin quartz plate 119 is locatedbetween the support plate 118 and the wafer support 116. The quartzeliminates arcing between the support plate 116 and other components inthe wafer processing chamber 110A. The quartz plate 119 is transparentto radiate energy provided by the lamps 130. This allows the lamps 130to quickly heat the wafer support 116.

The wafer support 116 is encircled by a quartz shield 150. The quartzshield 150 rests on the alumina support plate 118 (partially shown inFIG. 7) to extend above the wafer support 116 and define a waferreceiving pocket within which both the wafer support 116 and the wafer114 reside. The quartz shield 150 has its upper edge chamfered outwardsto receive the wafer 114 more easily when the wafer 114 is transferredto and from the wafer support 116. The quartz shield 150 primarilyfunctions to shield the edge of the wafer support 116 from attracting anarc.

In processing, the temperature of the wafer support 116 is measured by athermocouple 152 mounted in the wafer support 116. The thermocouple 152is mounted within an alumina nitride sheath 154 which snugly fits withinthe body of the wafer support 116. The sheath 154 provides electricalinsulation between the thermocouple 152 and the body of the wafersupport 116. Although the sheath 154 is electrically highly resistive,it remains a good conductor of heat. The sheath 154 has a low thermalmass and thus low thermal inertia making it suitable for use with thethermocouple 152. Further, the sheath 154 is chemically stable withinthe processing environment of the processing chamber 112.

The thermocouple 152 is connected to the temperature determinationdevice 140 by an electrically conductive cable 156. As will be describedbelow, the cable 156 passes along a central portion of the support arm122 and is electrically insulated from any radio frequency energy withinthe processing chamber 112.

The thermocouple 152 is held in position by a small nickel sphere 158which is crimped over the conductive cable 156. The sphere 158 isretained in a slot 160 formed in a keyed ceramic retaining element 162.The keyed retaining element 162 keys into a groove 164 formed in acentral protruding stub 166 on the underside of the wafer support 116.This arrangement ensures that the thermocouple 152 can be removedrelatively easily and replaced once the wafer support 116 is separatedfrom the support arm 122. The above-described arrangement ensures thatthe thermocouple 152 is held firmly in place within the body of thewafer support 116, while maintaining electrical isolation between thewafer support 116 and the thermocouple 152.

The wafer support 116 is secured to the support arm 122 by a pair ofbolts 168, which screw into the central stub 166. FIG. 8 show that thesupport arm 120 is primarily constituted by an inverted U-shaped ceramicsection 170. The bolts 168 pass through respective holes 172 passingthrough the horizontal portion of the U-shaped section 170. To preventexcessive bearing of the bolts 168 onto the horizontal portion of theU-shaped section 170, each head is spaced from the horizontal portion bymeans of a Belvedere spring washer 174. Preventing excessive bearing ofthe head of the bolt 168 onto the ceramic U-shaped section 170 isimportant, since ceramic, particularly thin section ceramic, isrelatively brittle. Excessive bearing force may cause the U-shapedsection 170 to break.

An rf conductive strip 180 passes along the support arm 122. The strip180 is electrically connected to the underside of the wafer support 116at the stub 166. The rf conductive strip 180 is coated with a hightemperature elastomeric dielectric material, such as polyimide, such asmaterials available from Dupont Electric under the trade name Pyralin.

This polyimide coating provides an electric insulation for the rfconductive strip 180. In addition, the rf conductive strip 180 iselectrically isolated from the conductive cable 156 by means of aceramic isolator 182. The details of the ceramic isolator will bediscussed below with reference to FIGS. 10(a) and 10(b). Further, the rfconductive strip 180 is isolated from the interior of the processingchamber 112 by the "legs" of the inverted U-shaped section 170 and byisolator 184. The details of isolator 184 will be described below withreference to FIG. 11(a) and 11(b).

During assembly, the thermocouple 152 and its associated sheath 154 isinserted into the wafer support 116. The thermocouple's lead cable 156is then fed into the U-shaped section 170. The wafer support 116 isfastened onto the U-shaped section 170, by means of bolts 168. Theisolator 182 is placed over the conductive cable 156 to isolate theconductive cable 156 from the rf strip 180. The rf conductive strip 180is then laid onto isolator 182, and isolator 184 is positioned over therf conductive strip 180.

Thereafter, a flat ceramic retainer 186 is slotted into grooves 188formed close to the free ends of the "legs" of the U-shaped section 170.The retainer 186 acts as a retainer for all the various pieces which arelocated within the body of the U-shaped section 170. The details of theretainer 186 are shown in FIG. 12.

As illustrated in FIGS. 9(a) and 9(b), the support arm 122 isconstituted by a relatively slender central portion with enlargedportions at its free and fixed ends, 120 and 124, respectively. The freeend 120 of the support arm 122 has two bolt holes 172 formedrespectively on either side of a slot 190 formed in the upper surface ofthe free end 120. This slot 190 receives a keyed formation 192 extendingdownward from the stub 166 on the bottom of the wafer support 116. Thiskeyed formation 192 mates with the slot 190 and further stabilizes thewafer support 116 when it is positioned on the support arm 122. Thedetails of the keyed formation 192 are shown in FIGS. 8 and 14. Thefixed end 124 of the support arm 122 is secured to a vertically movablestem 194, the details of which will be described with reference to FIG.13.

From FIGS. 10(a) and 10(b) it can be seen that the isolator 182 is inthe form of a U-shaped channel within which conductive cable 156 rests.The U-shaped channel has an enlarged portion 196 formed at one end. Theenlarge portion 196 covers the rf conductive strip 180 at the fixed end124 of the support arm 122.

As shown in FIGS. 11(a) and 11(b), the isolator 184 has an enlargedportion 198 which is sized to fit relatively snugly within the free end120 of the support arm 122 The enlarged portion 198 has a channel 200formed therein. When the apparatus is assembled, the rf conductive strip180 lies on the upper surface 202 of the insulator 184. The rfconductive strip 180 also bends to follow the internal contour of thechannel 200. This arrangement is illustrated in FIG. 7 and provides forseparating the rf conductive strip 180 from the connecting bolts 168. Ascan be seen from FIG. 7, a suitable spacer element 204 is provided tofit into the channel 200 and provide isolation between the rf conductivestrip 180 and the bolts 168.

The details of the retainer 186 are illustrated in FIG. 12. The retainer186 is generally spoon-shaped with an enlarged portion 206 sized to bereceived within the groove formed at the free end 120 of the support arm122. During assembly, the retainer 186 is inserted into the slot 188from the free end 120 of the support arm 122.

The fixed end 124 of the support arm 122 is connected to the stem 194 asillustrated in FIG. 13. The stem 194 is a hollow tube which flares atits upper end to define flanges 210 to which the fixed end 124 of thesupport arm 122 is bolted by bolts 212. To prevent excessive bearingforce between the bolts 212 and ceramic fixed end 124, a Bellevillespring washer 214 is provided between each bolt 212 and the fixed end124 of the support arm 122.

A stainless steel bellows 216 is positioned between the flanges 210 andthe lower wall of the processing chamber 112. The bellows 216 allow thesupport arm 122 to be moved vertically up and down, while at the sametime providing a seal around the stem 194 as it passes through the wall218 of the processing chamber 112.

As indicated previously, the stem 194 is in the form of a hollow tube.An electrically non-conductive tube 220 is located inside the tubeforming the stem 194. The non-conductive tube 220 is typically made of apolyimide material and provides electrical isolation between theprocessing chamber 112 and a hollow rf conducting tube 222. The rfconducting tube 222 is connected to the rf source 142 and the rfconductive strip 180. The conductive cable 156 communicating between thethermocouple 152 and the temperature determination device 140 passesdown the central bore formed in the rf conductive tube 222.

FIG. 14, when read with FIG. 13, illustrates how the connection is madebetween the rf conductive strip 180 and the rf conductive tube 222. Asshown in FIG. 13, the rf conductive tube 222 flares at its upper end todefine a circular flange 224. The rf conductive strip 180, asillustrated in FIG. 14, ends in a circular conductive hoop 226. When thesupport arm 122 is assembled, the hoop 226 is placed on the circularflange 224 of the rf conductive tube 222.

This provides a rf conductive connection to the rf conductive strip 180which is coupled to the wafer support 116. This connection allows foreasy assembly and disassembly of the support art 122. The connectionalso allows for a certain amount of rotational freedom (above thelongitudinal access of stem 194) when the fixed end 124 of the supportarm 122 is being positioned onto the flange 210 of the stem 194.

4. The Matching Network

In accordance with the present invention, the rf source 142 is coupledto both the wafer support 116 and the showerhead 136 through a matchingnetwork 145. The matching network 145 is a resistor/inductor/capacitornetwork. The matching network 145 matches the load impedance to thesource impedance, in order to maximize the power delivered by the sourceat a given frequency. The matching network 145 also splits rf powerbetween the wafer support 116 and the showerhead 136 and sets the phaseshift of the rf signals provided to the showerhead 136 and the wafersupport 116.

A matching network 145 used in one embodiment of the present inventionis illustrated in FIG. 15A. The matching network 145 shown in FIG. 15Aincludes a load match transformer 70, two inductors 80 and 82, and twocapacitors 72 and 74. The load match transformer 70 is coupled at oneend to the rf source 142 and ground, and on another end to the inductors80 and 82. The inductors 80 and 82 are coupled to the showerhead 136 andwafer support 116, respectively, through capacitors 72 and 74,respectively.

The load match transformer 70 may have a primary to secondary turnsratio ranging from 1:1 to 1:4, with 1:1.22 being typical. In accordancewith the present invention, the primary coil of the load matchtransformer 70 may have 18 turns, and the secondary coil of the loadmatch transformer 70 may have 47 turns. The inductors 80 and 82 eachhave an inductance of 50 :H, and the capacitors 72 and 74 each have acapacitance of 0.01:F.

The power split and the phase shift between the rf signals at theshowerhead 136 and wafer support 116 may be altered by modifying theturns ratio of the load match transformer 70. Alternatively, as shown inFIG. 15B, a load match transformer 71 may have a selectable ground tap78. The selectable ground tap 78 allows for the selection of variableground tap positions to change the power split and phase shift betweenthe rf signals at the showerhead 136 and the wafer support 116.

Yet another embodiment of the matching network 145 is shown in FIG. 15C.Capacitor 72 and the showerhead 136 are both coupled to ground throughan inductive choke 83. Capacitor 74 and the wafer support 116 are bothcoupled to ground through an inductive choke 84. Inductive choke 83 andinductive choke 84 may each have a value of 500 :H. When such anembodiment is employed, the showerhead 136 and the wafer support 116 donot become DC biased.

Coupling both the showerhead 136 and the wafer support 116 to the rfsource 142 through the matching network 145 is advantageous when theprocessing chamber 110 is employed for plasma annealing and/oroxidation. The phase shift between the rf signals at the showerhead 136and the wafer support 116 may be set to provide for enhancing theuniformity of a plasma generated during post-deposition processing. Anout of phase relationship between the showerhead 136 and the wafersupport 116 signals causes the ions in the plasma to be more attractedto the wafer support 116 than the grounded processing chamber 112. Theout of phase relationship also increases the voltage potential betweenthe showerhead 136 and the wafer support 116, thereby enhancing theuniformity of the ion flux towards the wafer 114.

Adjusting the power split of the signals at the showerhead 136 and thewafer support 116 enables the intensity of ion bombardment of the wafer114 and the showerhead 136 to be controlled. Negative biasing of thewafer support 116, during plasma generation, generally causes ions toincrease their acceleration towards the wafer 114. Excessive negativebiasing of the wafer support 116 causes ions to bombard the wafer 114with such energy that the wafer 114 becomes damaged. Excessive negativebiasing of the showerhead 136, during plasma generation, generallycauses ions to bombard the showerhead 136 and create contaminantparticles.

In embodiment of the present invention, the power split of the rfsource's 145 signal may be selected by a chamber 110A operator. Thepower split may be set so that the negative biases of the showerhead 136and the wafer support 116 minimize the potential for the aforementionedcontamination and wafer damaging ion bombardment.

In accordance with the present invention, the matching network 145 maybe configured to supply rf signals to the wafer support 116 and theshowerhead 136 having the same power and frequency, but being 180degrees out of phase. This efficiently couples rf power to theshowerhead 136 and the wafer support 116 for transforming gases in theprocessing chamber 112 into plasma.

Embodiments of an rf split power configuration may be seen by referenceto U.S. Pat. No. 5,314,603, entitled PLASMA PROCESSING APPARATUS CAPABLEOF DETECTING AND REGULATING ACTUAL RF POWER AT ELECTRODE WITHIN CHAMBERand issued to Sugiyama, et al., or to U.S. Pat. No. 4,871,421, entitledSPLIT-PHASE DRIVER FOR PLASMA ETCH SYSTEM and issued to Ogle, et al.

5. Chamber Operation

During a deposition process, the gas panel controller 50 causes the gaspanel 52 to supply a CVD process gas, such as TDMAT for TiN depositionor a combination of ethyliminoethyl(C,N)tris(diethylamido)tantalum andethylimidotris(diethylamido)tantalum for TaN deposition, to theshowerhead 136. Through the showerhead 136, the process gas isintroduced into the processing chamber 112 and transported to the heatedwafer 114. As a result, a thin film of material deposits on the uppersurface of the wafer 114. When TDMAT is employed, the thin film ofmaterial that is formed is titanium nitride TiN. When a combination ofethyliminoethyl(C,N)tris(diethylamido)tantalum andethylimidotris(diethylamido)tantalum gases are used, the thin filmdeposition is a tantalum nitride TaN film.

During a post-deposition process that is performed in the semiconductorwafer processing chamber 110A, annealing, oxidation, or exposure tosilicon may be performed, as will be described below. During a plasmaannealing process, a plasma gas, such as nitrogen, hydrogen, argon, or acombination thereof is supplied to the showerhead 136 by the gas panel52 under control of the gas panel controller 50. During apost-deposition oxidation process, an oxygen based gas, such as O₂ or aN₂ /O₂ mixture is supplied to the showerhead 136 by the gas panel 52under control of the gas panel controller 50. During a silicon exposureprocess, a silicon based gas, such as silane (SiH₄), is supplied to theshowerhead 136 by the gas panel 52 under control of the gas panelcontroller 50.

In both the plasma annealing process and the oxidation process, the gassupplied by the showerhead 136 is transformed into a plasma containingpositively charged ions that react with the wafer 114. In the siliconexposure process, the gas is infused with energy through the heating ofthe wafer 114 and wafer support 116. Any carrier gas that is employedduring either the deposition or post-deposition processing, as well asany by-products from the deposition or post-deposition processing, areexhausted from the processing chamber 112 by the pressure control unit157.

6. Alternative Chamber Configurations

FIG. 16 illustrates a semiconductor wafer processing chamber 110B thatincorporates an alternative embodiment of the present invention forcarrying out a process in accordance with the present invention. Thesemiconductor wafer processing chamber 110B shown in FIG. 16 is the sameas the chamber 110A depicted in FIG. 5, except that the showerhead 136is not coupled to an rf source. An rf source 62 is coupled to the wafersupport 116 through a matching network 63, and the showerhead 136 isgrounded.

The matching network 63 uses conventional means for matching the loadimpedance of the wafer support 116 to the impedance of the rf source 62.The matching maximizes the power delivered by the rf source 62 at agiven frequency. In accordance with the present invention, the matchingnetwork 63 and rf source 62 may be configured to supply an rf signal tothe wafer support 116, so that sufficient rf energy is provided forplasma annealing or oxidation without causing the wafer 114 to becomeexcessively negative biased.

FIG. 17 illustrates a semiconductor wafer processing chamber 110C thatincorporates an alternative embodiment of the present invention and iscapable of carrying out a process in accordance with the presentinvention. The semiconductor wafer processing chamber 110C in FIG. 17 isthe same as the chamber 110A depicted in FIG. 5, except that theshowerhead 136 and the wafer support 116 are each coupled to a differentrf source 143 and 144, respectively. Rf source 143 is coupled to theshowerhead 136 through matching network 146, and rf source 144 iscoupled to the wafer support 116 through matching network 147.

The matching networks 146 and 147 each use conventional means formatching the load impedance of the showerhead 136 and wafer support 116,respectively, to a source impedance. The matching maximizes the powerdelivered by each source at a given frequency. Preferably, the rfsources 143 and 144 are coupled together (not shown) to provide forcontrolling the phase shift and power split between the rf signalsprovided to the showerhead 136 and the wafer support 116. In accordancewith the present invention, the matching networks 146 and 147 and rfsources 143 and 144 may be configured to supply rf signals to the wafersupport 116 and the showerhead 136 that have the same power andfrequency, but are 180 degrees out of phase.

In yet another embodiment of the present invention, the wafer support116 in any of FIGS. 5, 16, or 17 may be a resistive heater. Theresistive heater supports the wafer 114 and incorporates a resistivecoil for heating the wafer 114.

The semiconductor wafer processing chambers shown in FIGS. 5, 16, and 17may be employed to carry out a number of processes. In a further aspectof the present invention, a process is provided for forming a diffusionbarrier. It will be recognized that the process of the present inventionmay be advantageously performed in the aforementioned apparatuses.However, it should be further recognized that the disclosed method maybe performed in any number of suitable chambers.

B. Film Construction

1. Overview

Embodiments of the present invention provide for the construction of afilm with an improved resistivity value in an integrated circuit. Onefilm that may be constructed is a diffusion barrier. However, otherfilms that are intended to inhibit the diffusion of contact metals, suchas aluminum and copper, may also be constructed using embodiments of thepresent invention.

In accordance with the present invention, a layer of material isdeposited on a substrate, such as a semiconductor wafer. The material isthen plasma annealed to reduce the resistivity of the depositedmaterial. Subsequently, a new layer of the material is deposited on thepreviously deposited material. The material is once again annealed toreduce the material's resistivity. The deposition and annealing of thematerial may be repeated several times to form a film that resides onthe upper surface of the wafer.

Another aspect of the present invention provides for the annealedmaterial on the wafer to be stuffed with molecules. The stuffingenhances the materials ability to inhibit the diffusion of contactmetals, such as aluminum or copper. In order to enhance the filmsoperation as a barrier to aluminum, the stuffing may be achieved throughoxidation of the annealed material. In order to enhance the filmsoperation as a barrier to copper, the stuffing may be achieved throughexposing the annealed material to silane (SiH₄). Alternatively, reduceddiffusion of copper may be obtained by depositing a material that is aternary metal silicon nitride.

Yet another aspect of the present invention provides for the deposition,annealing, and stuffing of the material on the wafer to be performedin-situ.

2. Annealing to Lower Film Resistivity

In accordance with the present invention, a film may be formed on awafer by depositing a layer of material on the wafer and plasmaannealing the layer of material, so as to reduce its resistivity.

The layer of material is deposited on a wafer in a chamber that iscapable of performing a traditional chemical vapor deposition, such aschamber 10 in FIG. 3(a), chamber 110A in FIG. 5, chamber 110B in FIG. 16or chamber 110C in FIG. 17. The deposition of a titanium nitridematerial may be achieved through the use of a metallo-organic titaniumcompound, preferably tetrakis(dialkylamido) titanium (Ti(NR₂)₄).Alternatively, a deposition of tantalum nitride material may be achievedthrough the use of a metallo-organic tantalum compound or a combinationof compounds, e.g., a combination ofethyliminoethyl(C,N)tris(diethylamido)tantalum andethylimidotris(diethylamido)tantalum.

A carrier gas, such as helium, argon, nitrogen, or hydrogen, brings thetitanium or tantalum compound into the chamber. In the chamber, thetitanium compound or tantalum compound is reacted with remotelygenerated reactive species, such as halogen, ammonium or hydrogenradicals. To facilitate the deposition of either titanium nitride ortantalum nitride, the wafer temperature is set to be about 200-600° C.,and the processing chamber pressure is set to be about 0.1-100 Torr.

The deposited titanium nitride or tantalum nitride contains significantamounts of carbon, thereby causing the resulting film to be chemicallyreactive. Consequently, oxygen is absorbed into the film, when the filmis exposed to air or other oxygen containing gases. Since the oxygenabsorption is uncontrolled, the stability of the film is impaired andthe resistivity of the film is adversely increased. This may result inthe reliability of devices formed on the wafer being poor.

After exposure to air, the sheet resistivity of the deposited film canincrease to values of about 10,000 μΩ-cm/sq up to about 100,000μΩ-cm/sq. This is highly undesirable when the deposited titanium nitrideor tantalum nitride is operating as a barrier layer for conductivecontacts and vias. For a barrier layer, a resistivity on the order ofabout 1,000 μΩ-cm or less is desirable.

In accordance with the present invention, the deposited film is plasmaannealed with an inert plasma containing high energy ions. The ions areobtained by applying a DC bias voltage to the wafer. The DC bias voltagemay be applied to the wafer by a low power rf source coupled to thewafer support and providing sufficient power to form a plasma from aprecursor gas. The application of a voltage of about 100 to 1,000 voltsto the wafer is sufficient. For example, 400 volts having only 100 wattsof rf power may be applied to form a plasma. This is sufficient toproduce high energy ions and to passivate or densify a titanium nitrideor tantalum nitride film so that it remains stable overtime.

When titanium nitride or tantalum nitride films that are annealed inaccordance with the present invention are exposed to air, oxygen, orwater vapor, the oxygen is either not absorbed or absorbed to a muchlesser extent than if no bias voltage had been applied to the wafer.Both titanium nitride films and tantalum nitride films deposited andannealed in accordance with the present invention are more crystalline,contain more nitrogen, and have a reduced oxygen and carbon contentcompared to titanium nitride or tantalum nitride films that are producedby the conventional thermal CVD of metallo-organic titanium compounds.The deposited films that are annealed according with the presentinvention also have a low and stable sheet resistivity.

The exact mechanism of the present invention is not known. However, itis believed that the high energy ion bombardment of the depositedmaterial on a biased substrate densifies the film.

a. Nitrogen Plasma

In one embodiment of the present invention, the gas used to form theplasma for the annealing of deposited titanium nitride may be any gas,but is preferably a non-oxygen-and-carbon containing gas such asnitrogen, ammonia, or argon. Nitrogen is the most effective forpassivation of the titanium nitride material. Alternatively, thedeposited material can be bombarded with ions generated from anongaseous species, such as ion sources. The plasma treatment of thedeposited titanium nitride does not adversely affect particleperformance, step coverage, deposition rate or barrier performance ofthe deposited material.

Titanium nitride has been deposited on a silicon wafer under thefollowing conditions in a conventional vacuum chemical vapor depositionchamber 10. The pressure in the processing chamber 12 was 0.45 Torr, andthe wafer support 16 was set to a temperature of 420° C. A helium flowof 400 sccm was used through a bubbler containing Ti(NR₂)₄, and a flowof nitrogen dilutant was set at 100 sccm. An argon purge gas was flowedin the processing chamber at 200 sccm following the deposition of thetitanium nitride. A conventional CVD process for depositing titaniumnitride is disclosed in U.S. Pat. No. 5,246,881 issued to Sandhu, et al.

As a result, titanium nitride was deposited at a deposition rate ofabout 425 Å per minute. The resultant titanium nitride film was veryuniform in thickness, having a four wafer thickness variation of only3.03%. However, the sheet resistivity (average of 4 wafers) was high at11,360 μΩ-cm/sq. The resistivity was also unstable.

FIG. 18 is a graph of sheet resistivity of the deposited titaniumnitride in Ω/sq versus time in hours. The measurements denoted by a □were taken from films withdrawn from the deposition chamber after thedesired film thickness was obtained. The measurements denoted by a ◯were taken from films cooled to a temperature of 150° C. prior toremoving them from the deposition chamber. Although the sheetresistivity of the □ films is lower than those of the ◯ films, bothfilms are unstable, and the sheet resistivity increases with time. Theseproperties are undesirable for a diffusion barrier.

Rutherford backscattering measurements were made on the depositedtitanium nitride film. The resulting spectrum is given in FIG. 19. Thepeaks for carbon, C, nitrogen, N, and oxygen, O, are marked on thespectrum, as is the silicon interface. The content of various materialin the titanium nitride is as follows: carbon content about 30%,nitrogen content about 24%, oxygen content about 25%, and titaniumcontent about 23%. This shows that the deposited titanium nitridematerial contains comparatively high levels of carbon and oxygenimpurities.

In an effort to reduce the titanium nitrides sheet resistivity, thedeposition method of the titanium nitride was varied by the addition ofvarious gases during the deposition procedure. The results are given inTable I, which appears in FIG. 20. The Control layer of titanium shownin Table I was deposited using the method set forth immediately above.The most successful run of reducing the sheet resistivity of thetitanium nitride included a flow of NF₃ (7 sccm) during deposition. Thisreduced the sheet resistivity to 2,200 μΩ-cm. However, Rutherfordbackscattering spectra of the NF₃ treated material (see FIG. 23) showsthat fluorine is incorporated as an impurity in the film. Theincorporation of the fluorine is undesirable.

Next, pre- and post-deposition flow of gases and plasma treatment wereused to determine whether such treatment would affect the sheetresistivity of a deposited titanium nitride. In two cases, a plasma wasinitiated before and after chemical vapor deposition of titaniumnitride. The plasma was generated using a low power of 100 watts andwithout biasing the substrate silicon wafer receiving the titaniumnitride deposition. The results are summarized in Table II, whichappears in FIG. 21. None of the pre- and post-deposition treatments hadmuch effect on the sheet resistivity of the deposited titanium nitride.Thus, it was highly unexpected that the application of a bias voltage tothe wafer in a plasma would decrease the sheet resistivity and cause itto remain stable over time.

Aspects of the present invention will be further described by means ofthe following examples, but the invention is not meant to be limited tothe details described therein. A series of tests was conducted in whicha bias voltage of 400 volts was applied to a silicon wafer substratehaving a layer of titanium nitride thereon. The titanium nitride wasdeposited on the wafer in a chamber such as chamber 110B of FIG. 16 andannealed with a plasma at an applied rf power of about 100 watts.Deposition and biasing owere cycled sequentially. The two steps werecycled up to five times. A summary of depositions thickness, number ofcycles and resistivity obtained over time are given Table III, whichappears in FIG. 22. The Control was deposited in five uninterruptedsteps, but without being annealed in a plasma between depositions.

The data in Table III shows that titanium nitride resistivity can bemarkedly reduced and stability dramatically improved by a postdeposition annealing of the titanium nitride. In each of the Examples inTable III, the resistivity and change in resistivity over time isimproved over the Control case. The initial resistivity of the annealedtitanium nitride is lower, and the resistivity increases less over time.

FIG. 24 is a graph an Auger analysis of the titanium nitride film ofExample 1. The graph displays the atomic concentration of elements inthe film versus the films sputter edge depth in angstroms. The titaniumnitride was biased twice for 30 seconds (see Table III above). As shownin FIG. 24, the titanium concentration remains steady, but the graphclearly shows that the film surface nitrogen concentration is high,while carbon and oxygen concentrations are low. This reduction in carbonand oxygen impurity levels continues for a depth of about 100 Å. At a400 Å depth, when the film was first annealed with high energy nitrogenions, the nitrogen concentration rises, while the carbon and oxygenconcentrations decrease. The graph of FIG. 24 also shows a change in theelemental composition of the film after annealing in accordance with thepresent invention. The change in elemental analysis with depth is shownin Table IV, which appears in FIG. 25.

Since a 100 Å thick layer of titanium nitride is adequate for a barrierlayer, the present post-deposition annealing is ideal for improving thestability and reducing the resistivity of titanium nitride barrierlayers. An Auger spectrum showing surface elements present on the postdeposition annealed titanium nitride of Example 7 is shown in FIG. 26.This spectrum shows that the bulk of material deposited is titaniumnitride with some titanium present. Carbon and oxygen are present at thesurface as impurities.

However, Auger sputtering analysis of the Example 7 film, as shown inFIG. 27, shows that the oxygen concentration drops markedly in the bulkof the film to a low level. Carbon is the only other major impuritybesides oxygen, but it remains unaffected by the present annealingprocess. In a depth of 200 Å, concentrations of various elements in thefilm in atomic percent are: oxygen, 2.8%; carbon, 20.9%; titanium 38.8%;and nitrogen, 37.5%. No silicon was present.

As a comparison, surface Auger analysis of the Control film is shown inFIG. 28, and sputter Auger analysis of the Control film is shown in FIG.29. The oxygen content of the Control film is significantly higher. At200 Å depth, the concentration of elements of the control film in atomicpercent are: oxygen, 10.8%; carbon, 20.7%; titanium, 41.0%; andnitrogen, 27.5%. No silicon was present.

Surface Auger analysis of the titanium nitride film of Example 8 isshown in FIG. 30, and sputter Auger analysis versus depth in angstrom isshown in FIG. 31. The oxygen content of this film was low. At 43 Ådepth, the concentration of elements in atomic percent are: oxygen,3.1%; carbon, 13.7%; titanium, 40.0%; and nitrogen, 43.2%. No siliconwas present.

Rutherford backscattering was used to determine the density in atoms/cm³of the Control and Example titanium nitride deposited films. The data issummarized in Table V, which appears in FIG. 32. As seen from the datain Table V, plasma annealing, including the bombardment of the depositedtitanium nitride with high energy ions, increases the density of thetitanium nitride film as compared to the Control film.

The present invention is not limited to titanium nitride barrier layers.The present invention may also improve properties and chemicalcompositions of other materials such as aluminum, copper, tantalum,tantalum pantoxide, silicides, other nitrides. For example, propertiesand chemical compositions of binary metal nitride M_(x) N_(y) andternary metal silicon nitride M_(x) Si_(y) N_(z) (where M may be Ti, Zr,Hf, Ta, Mo, W and other metals) may be improved by practicing aspects ofthe present invention. Substrates other than a silicon wafer can also beused such as stainless steel, metals, oxides, glasses, and silicides.

The deposition and plasma annealing can be performed in a single CVDchamber fitted with a precursor gas and plasma capability, such aschambers 110A, 110B and 110C. When employing chamber 110A, 110B, or110C, films of titanium nitride can be deposited and directly thereafterannealed in the same chamber. Alternatively, more than one chamber maybe employed when an apparatus such as the one shown in FIG. 3(a) isemployed in practicing the present invention. When more than one chamberis employed a vacuum is preferably maintained during the transfer of thesubstrate from the CVD chamber 10 to an annealing chamber.

The following procedure may be followed when the plasma annealing ofdeposited titanium nitride is performed in chamber 110B. The wafer 114resides on the wafer support 116 and is spaced about 0.3 to 0.8 inches,preferably 0.6 to 0.7 inches, from the showerhead 136. Energetic ionsare obtained by applying rf energy to the substrate from the rf signalsource at about 350 KHz at a power of 100 to 500 watts. This translatesto about 0.3 to 1.6 watts of power per square centimeter (CM²) ofsurface area of the wafer 114.

With the negatively powered wafer support 116 and the showerhead 136 andchamber walls grounded, a DC self-bias voltage between 50 to 1,000 voltsis induced. Preferably, the DC self-bias voltage is between 200 to 800volts, between the wafer 114 and ground. This is sufficient to attractions to impact the wafer 114 surface at high energy. As a result, thedeposited titanium nitride is passivated or densified so that it remainsstable over time.

FIG. 33 is a graph of atomic oxygen concentration versus air exposuretime for two different layers of titanium nitride formed in accordancewith the present invention. Both titanium nitride films were depositedand plasma annealed in the same chamber. The chamber was similar tochamber 110B, which is described above.

For each film, a 200 Å thick titanium nitride film was formed by cyclingdeposition and annealing. To do this, a 100 Å layer was deposited andthereafter annealed, followed by the deposition and annealing of asecond 100 Å layer. Annealing was achieved using an N₂ plasma. Thepercentage of atomic oxygen concentration was measured for the two filmsrepeatedly over a period of over 24 hours and is reflected by plot 312.

As can be seen from plot 312, the concentration of oxygen was initiallyabout 2%. After 24 hours, the content was less than 2.5%, indicatingthat the deposited films were very stable. By comparison, plot 314illustrates an oxygen concentration measurements taken on titaniumnitride films deposited using conventional CVD without annealing. Notonly did these films have a higher (15%) initial oxygen concentration,but they also absorbed oxygen at a greater rate. The conventionallyformed films were also less stable with marked increases in resistivityover time. For comparison, point 316 in FIG. 34 illustrates the typicaloxygen concentration (about 1%) of a titanium nitride film deposited byphysical vapor deposition.

FIGS. 34(a)-(c) are graphical representations of XPS Spectra ondifferent films. FIG. 34(a) represents a spectrum of a 200 Ånon-annealed film and shows that the organically bonded carbon level, at316, is relatively high. By comparison, the measurements on a 200 Å filmused to produce FIGS. 34(b) and (c) show reduced organically bondedcarbon content at 317 and 318 respectively. It should be noted that thefilm used for FIG. 34(b) was formed by depositing a 100 Å layer oftitanium nitride, plasma annealing it according to the present inventionand thereafter depositing and annealing a second 100 Å layer of titaniumnitride. FIG. 34(c), was formed by successively depositing and annealingfour 50 Å thick layers of titanium nitride.

FIGS. 35(a) and (b) further illustrate the improvements of the presentinvention. FIG. 35(a) shows the resistance of vias employing a CVDtitanium nitride film that was deposited iand plasma annealed with a N₂plasma. The vias were first lined with a CVD titanium nitride adhesionlayer and then filled with a CVD Tungsten plug. FIG. 35(a) provides agraph of via resistance versus film deposition thickness. The graph wasprepared for a 0.5 :m via with an aspect ratio of approximately 2.5. Asshown the via resistance is substantially less for the plasma annealedfilm (plot 320) than for the non-annealed conventionally deposited film(plot 322). For comparison, the via resistance of a PVD depositedtitanium nitride film is illustrated by arrow 324.

Similar improvements are illustrated by the graph in FIG. 35(b), whichis a representation of salicide contact resistance versus titaniumnitride thickness. The graph is plotted for a 0.5 m contact with anaspect ratio of approximately 2.5. Plot 330 shows a resistance of thecontact prepared by an N₂ plasma treatment according to the presentinvention. Plot 330 illustrates a substantially lesser resistance thanthe resistance illustrated by plot 332, which represents a contactresistance resulting from a conventional prior art CVD deposition. Forcomparison, a PVD titanium nitride control contact resistance is givenby arrow 334.

FIG. 36 illustrates the effect of the number of cycles of deposition andannealing used to create a single film of a desired thickness. In FIG.36, a titanium nitride film having a total thickness of 200 Å wasdeposited by chemical vapor deposition and annealed with a N₂ plasma. Ina first case, illustrated by plot 340, the process was cycled four timeswith each of the four layers being deposited with a 50D thickness andplasma annealed prior to the deposition of a subsequent layer. In asecond case, illustrated by plot 342, two layers, each of 100 Å, weredeposited and individually annealed.

The case represented by plot 340 shows a lower resistivity (500 to600-cm) than the case represented by curve 342 (700 to 800-cm). However,the resistivities of the films represented by both plots 340 and 342 arebelow the upper limit of 1000 m-cm. Also, the increased resistivity ineach case over a period of eight days was approximately the same forboth cases at less than 5%.

Further tests were conducted to determine the effect of plasma treatmentprocess pressure on a film resistivity and DC bias voltage. The resultsof these tests are illustrated in FIG. 37. FIG. 37 is prepared for a 200Å titanium nitride deposition which was treated for 60 seconds in aplasma for which the applied power was approximately 20 watts.

As shown by plot 350, the improved resistivity exhibited by filmsproduced by the process of this invention is generally not dependent onthe process pressure. However, it appears that low resistivities werenot achieved when process pressures were lower than about 200 mTorr.

As illustrated by plot 352, the DC bias induced across the plasmadecreased fairly substantially as the process pressure was increasedfrom about 200 to 1000 mTorr. Thereafter, it remained relativelyconstant at about 150 volts.

FIG. 38(a) illustrates the effects of treatment duration and frequencyon film resistivity. Four different films, each having a total thicknessof 200 Å, were compared. One film, represented by plot 360, was formedby initially depositing and annealing a 50 Å layer and thereafterdepositing and annealing six 25 Å layers. Each of the layers wasdeposited and thereafter annealed prior to a subsequent layersdeposition. A second film, represented by plot 362, was formed byrespectively depositing and annealing four 50 Å layers. The third film,represented by plot 364, was formed by respectively depositing andannealing two 100 Å layers. The final film, represented by plot 366, wasformed by depositing a single 200 Å layer which was thereafter annealedaccording to the invention.

From the plots in FIG. 38(a), a number of observations can be made. Itappears that lower resistivities are achieved when a greater number ofindividual layers make up the final layer. Also, the thinner theindividual layer is, the less effect the time of plasma treatment has onthe resistivity. FIG. 38(b) illustrates another example of the effect ofplasma treatment time on film resistivity.

In addition to decreasing the resistance and increasing the stability ofthe films, it may be possible to use the method of the present inventionfor other purposes. Analysis of films annealed using a N₂ plasma haveshown an increase in the amount of nitrogen close to the surface of thefilm. It appears that some of the nitrogen ions have become embedded inand have reacted with the film. Thus, it may be possible to use thisannealing process to enrich a film with ions/molecules from the plasma.Further, this process could be used to eject or replace unwantedmolecules/ions from the film. FIGS. 34(b)-(c) show that ions impactingthe film eject carbon atoms.

b. Nitrogen/Hydrogen Plasma

In an alternative embodiment of the present invention, a mixture ofnitrogen and hydrogen may be employed for generating a plasma during theplasma annealing of a film deposited on a wafer 114. As a first step, atitanium nitride film is deposited on the wafer 114 using conventionalthermal CVD processing. Thereafter, the deposited material is annealedusing a plasma that is generated from a gas having a mixture of nitrogenand hydrogen.

If any one of chambers 110A, 110B or 110C are employed in performingthese steps, the CVD processing and annealing may be performed in thesame chamber. Alternatively, titanium nitride can be deposited on thewafer 114 in one chamber, and the wafer 114 can be transferred intoanother chamber for post-deposition plasma annealing.

When employing chamber 110A, the wafer 114 may be placed on wafersupport 116 and spaced about 0.3 to 0.8 inches, preferably 0.6 to 0.7inches, from the showerhead 136. As described above, a layer of titaniumnitride film may be deposited on the wafer 114. The initially depositedtitanium nitride layer may be 50 to 200 Å thick.

After the deposition has been completed, plasma annealing of thedeposited material commences. A gas comprised of a 3:1 mixture ofnitrogen and hydrogen is introduced into the processing chamber 112 viathe showerhead 136. The mixture of nitrogen and hydrogen is introducedwith a nitrogen flow rate of about 300 sccm. The rf source 142 thensupplies 350 watts of rf power at 350 KHz through the matching network145 to produce rf signals to the wafer support 116 and the showerhead136. Preferably, the rf signals at the showerhead 136 and the wafersupport 116 are 180 degrees out of phase.

Although the above-described gas mixture has a nitrogen to hydrogenratio of 3:1, any ratio between 3:1 and 1:2 may be used. Generally, ahigher portion of hydrogen in the mixture results in a film with greaterlong-term stability. However, too much hydrogen in the plasma whendepositing titanium nitride films may result in bonding between hydrogenand carbon in the film to form polymers, which increases the filmsresistivity.

A plasma containing positively-charged nitrogen and hydrogen ions formsunder the influence of the rf power supplied to the showerhead 136 andthe wafer support 116. The plasma is typically maintained for 10-30seconds. As described above, the processing chamber 112 is grounded. Theshowerhead 136 acquires a negative bias between -100 to -400 volts,typically -200 volts. The wafer 114 self-biases to acquire a negativebias of between -100 to -400 volts, typically -300 volts. This negativebias voltage remains approximately constant during a bombardment period.

During the bombardment period, positively charged ions from the plasmaare accelerated by the voltage gradient into the surface of the wafer114. This causes the ions to bombard the wafer surface, penetrating to adepth of 50 to 100 Å. Energetic neutral atomic particles from the plasmaalso may bombard the wafer 114.

As a result of the ion bombardment, compression of the depositedmaterial occurs and the thickness may be reduced by 20 to 50%. Thereduction depends upon the temperature of the wafer and the plasmatreatment time and energy. Further layers of titanium nitride may besuccessively deposited and annealed as desired. Preferably, each of thefurther layers has a thickness ranging from 50 to 100 Å.

After the annealing is completed, the resulting annealed titaniumnitride film exhibits many improved properties. Oxygen content isreduced from 20 to 25%, causing oxygen to comprise less than 1% of thedeposited and annealed material. The density of the film increases fromless than 3.1 grams per cubic centimeter (g/cm³) to about 3.9 g/cm³. Thefraction of carbon incorporated into the deposited film is reduced by25% or more, so that the carbon comprises 3% of the deposited film.Changes in the structure of the film occur, and the films resistivitydrops from pre-treatment levels of approximately 10,000-cm to as low as150-cm. When the annealed film is exposed to oxygen, air, or watervapor, oxygen is absorbed to a much lesser extent than if the depositedfilm were not annealed. The plasma annealing causes replacement ofcarbon and nitrogen in the as-deposited film with nitrogen from theplasma.

The addition of hydrogen to the plasma-forming gas has been found tosignificantly reduce the amount of carbon that coats the inside of theprocessing chamber 112 upon being ejected from the film by the ionbombardment. The reduction in the carbon coating of the processingchamber 112 is beneficial, because the carbon coating changes theimpedance of the chamber and makes the precise control of the plasmadifficult. The reduction in carbon coating results in the processingchamber 112 being used a greater number of times before requiringcleaning.

FIG. 39(a) is an Auger electron spectroscopic depth profile for atitanium nitride film formed by successively depositing and annealingtitanium nitride layers 100 D thick onto a silicon dioxide layer. As maybe seen from FIG. 39(a), the carbon and oxygen content are uniformthroughout most of the film, with carbon being at 9 atomic percent andoxygen being at 2 atomic percent. The resistivity of the annealedtitanium nitride film is about 250-cm.

FIG. 39(b) shows that further improvements were obtained by depositingand annealing 50 Å layers of titanium nitride. FIG. 39(b) is in Augerelectron spectroscopic depth profile for a titanium nitride film formedby successively depositing and annealing titanium nitride layers 50 Åthick on top of silicon dioxide. Once again, the carbon and oxygencontent are uniform throughout most of the film, with carbon being lessthan 3 atomic percent and oxygen being 1 atomic percent. The portions oftitanium and nitrogen are higher than in the 100 Å process. Theresistivity of this film is only 180-cm.

c. Nitrogen/Hydrogen/Noble Gas Plasma

In yet another embodiment of the present invention, the nitrogen andhydrogen gas mixture used to form an annealing plasma may also includeother gases such as argon, helium, and ammonia. The inclusion ofadditional noble gases also improves the ion bombardment treatments.Since argon atoms are heavier than helium atoms, the argon atoms mayprovide superior bombardment capabilities.

Further, it is envisioned that the composition of films composed ofmaterials other than titanium nitride may be altered in a similar mannerusing the present invention. Other gases may be added to the plasma inorder to alter the chemical composition of the film, either by becomingincorporated into the film or reacting with the impurities presenttherein. For example, NH₃ and CH₄ may be used. An oxygen-based plasmagas may be more appropriate for treating oxide films such as Ta₂ O₅.

While this invention has been described in terms of plasma bombardingCVD deposited films, this invention has applicability to PVD-depositedfilms. Further, this invention finds particular application in thetreatment of binary metal nitride M_(x) N_(y) and ternary metal siliconnitride M_(x) Si_(y) N_(z) (where M may be Ti, Zr, Hf, Ta, Mo, W andother metals).

The present invention may also be used to modify the morphology of filmsin an advantageous manner. Thin barrier materials may be subjected tothe high density ion bombardment of the present invention in order toenhance the uniformity of their grain orientation. Because theorientation of grains in an underlying layer affects the structure ofsubsequently deposited layers, the present invention provides for theability to modify and improve the morphology of sequentially depositedlayers by modifying the crystal structure and/or growth orientation ofthe underlying layer.

It is possible to control the morphology of multiple layers bydepositing a thin nucleation interface layer less than 50 Å thick,modifying it by high density ion bombardment, and then depositing thebulk or remaining film by standard techniques. The structure of theoverlying layer would be determined by the structure of the underlyingpreviously modified layer.

This can be illustrated with reference to FIG. 40. For a titaniumnitride film, it has been determined that the preferred crystal andorientation is <200>. It is speculated that the addition of hydrogen tothe plasma may improve the film by making it more crystalline. FIG. 40is an x-ray diffraction glancing angle scan of a conventional CVDtitanium nitride layer, 1000 Å thick, deposited on a silicon wafer. Thepoint on the curve indicating the number of grains oriented in the <200>direction is indicated by the label 300. As can be seen from the graph,there is no obvious TiN <200> peak. This is indicative of weakcrystalline TiN <200> in films formed using conventional CVD processes.

FIG. 41 is an x-ray diffraction glancing angle scan of a CVD titaniumnitride layer, 1000 Å thick, deposited on a silicon wafer and annealedin accordance with the present invention. The diffraction patternindicates that the film is micro-crystalline with a preferredorientation <200> increased noticeably, as indicated by the label 350.There are more grains oriented in nearly the <200> direction, in theinterval between 40 and 45 degrees. Additionally, the peak 310 in FIG.40 is significantly lower in FIG. 41.

d. Tantalum Nitride Deposition Using a Hydrogen Plasma

In another embodiment of the present invention, tantalum nitride isdeposited and then plasma annealed using a hydrogen plasma. The plasmaannealing process does not adversely affect particle performance, stepcoverage, deposition rate or barrier performance of the depositedtantalum nitride material.

In the preferred embodiment of the invention, the tantalum nitridematerial is deposited on a silicon wafer under the following conditionsin a conventional vacuum CVD chamberI10. The pressure in the processingchamberI12 is 2 Torr, and the wafer supportI16 is heated to atemperature of 450° C. A helium flow of 95 sccm is used through abubbler containing a precursor gas comprising a combination ofethyliminoethyl(C,N)tris(diethylamido)tantalum andethylimidotris(diethylamido)tantalum. The ratio ofethyliminoethyl(C,N)tris(diethylamido)tantalum toethylimidotris(diethylamido)tantalum within the mixture is one to four.A flow of nitrogen dilutant is also applied to the chamber at a flowrate of 100 sccm. An argon purge gas is flowed into the chamber at 200sccm following deposition of the tantalum nitride.

It is important to note that in ethylimidotris(diethylamido)tantalum adouble bond exists between a nitrogen atom and the tantalum atom,whereas the other three nitrogen atoms are singly bonded. This bondingstructure may provide a lower limit to the nitrogen-tantalum ratio thatis attainable, e.g., a ratio of one.

Using the foregoing recipe, tantalum nitride is deposited at a rate of7-10 Å/minute for a period of 225Iseconds. The resultant tantalumnitride film has a relatively uniform thickness and sufficient stepcoverage. The sheet resistivity of film prior to annealing is relativelyhigh, e.g., 4000 Ω-cm. The resistivity of the tantalum nitride filmprior to annealing is unstable and increases over time as the film isexposed to air.

FIG. 51 depicts a spectrum graphI5100 attained using a RutherfordBackscattering (RBS) measurement on the non-annealed tantalum nitridefilm. The peaks for carbon C, nitrogen N, oxygen O and tantalum Ta aremarked upon the spectrum. The content of various materials in thetantalum nitride prior to plasma annealing (graph 5100) is as follows:tantalum content about 23.1%, carbon content about 22.1%, nitrogencontent aboutI23.7%, and oxygen content about 31%.

FIG. 52 depicts an Auger depth profileI5200 of the tantalum nitride filmprior to annealing. Note that the concentrations of carbon and nitrogenare high relative to the concentration of tantalum within the film.

Next, to improve the resistivity and stability of the film, the tantalumnitride film is annealed for 100 seconds in a hydrogen H₂ plasma.Generally, the annealing process is accomplished in the same chamber asthe deposition process, e.g., a System 5114 containing a Precision 5000mainframe outfitted with a TxZ chamber as manufactured by AppliedMaterials, Inc. of Santa Clara, Calif. Although the invention ispreferably practiced within a single chamber, the invention could bepracticed in two separate chambers, i.e., a deposition chamber and aplasma annealing chamber.

The hydrogen plasma was generated in a 2 Torr atmosphere of hydrogenflowing into the process chamber at a rate of 300 sccm. During plasmaannealing, the wafer is maintained at approximately 450° C. Tofacilitate plasma formation, the chamber is driven with a 350 kHz RFsignal at approximately 900 watts. Under this power level, the waferwill &self bias™ to a voltage of approximately 50 to 1000 volts. Duringannealing, the showerhead that supplies the hydrogen is spaced from thewafer by approximately 450 mm.

The resultant tantalum nitride film has substantially improved sheetresistance as compared to the non-annealed film. FIG. 51 depicts a RBSgraphI5102 of the annealed wafer. The relative concentration of tantalumin the structure (graph 5102) has increased substantially as compared tothe non-annealed wafer (graph 5100). Specifically, the tantalumconcentration is about 36.7%, the carbon concentration is about 4.1%,the nitrogen concentration is about 32.5% and the oxygen concentrationis about 26.7%. Thus, as is necessary to reduce the resistivity of thefilm, annealing has raised the relative concentration of tantalum (i.e.,23.1% pre-annealing and 36.7% post-annealing) and lowered the relativeconcentration of carbon (22.1% pre-annealing and 4.1% post-annealing) ascompared to the non-annealed film. Additionally, an Auger depth profile5300 is depicted in FIG. 53 that shows a relative increase in tantalumconcentration with respect to the concentration of carbon within thefilm after annealing.

The film that was analyzed was deposited by first depositing a tantalumnitride film having a thickness of 25 Å and then annealing the film. Theannealing process thins the deposition from 25 Å to 18 Å. This processof deposition and annealing is repeated a plurality of times (e.g.,eight) to achieve a desired film thickness. Such a repetitive process,known as an 8×25 process, has been found to produce the best resistivityresults as compared to depositing a single thick film of tantalumnitride.

Various test wafers were processed in accordance with the foregoingteachings. During the tests, various combinations of RF power, processduration, number of process cycles, and the like were used in an attemptto determine a process that results in the best sheet resistivity. Theresistivity of the film was found to substantially decrease when the RFpower forming the hydrogen plasma was increased from 350 watts to 900watts. Additionally, using an 8×25 process generated a film resistivitythat was superior to a film produced using a 4×50 process. The bestsheet resistivity of approximately 621-cm was produced in a 151I Å thickfilm using an 8×25 process with a plasma power of 900Iwatts, where theannealing plasma was applied for 100 seconds after each 25 Å deposition.The sheet resistance in all the tests was measured using a Prometrix RS510 omnimap with a type-B probe.

3. Secuential Annealing

In order to further reduce the resistivity of a deposited film, theplasma annealing process may be altered in accordance with the presentinvention to include two sequential plasma annealing steps. The firstannealing step is performed with a plasma that is generated from agaseous mixture including nitrogen and/or hydrogen, as described above.The second plasma annealing step is performed to remove hydrogen fromthe annealed material, since hydrogens affinity for oxygen results inincreased resistivity.

The ions formed in the second plasma bombard the deposited and annealedfilm material, thereby causing hydrogen in the surface of the materialto be ejected from the film as a waste by-product. The reduction inhydrogen reduces the materials affinity for oxygen, which enables thefilm to have a lower resistivity and exhibit improved stability.

The gas used for forming the plasma in the second sequential annealingstep may be comprised of nitrogen or a mixture of nitrogen and eitherhelium, argon, or neon. Helium is preferred, since it enhances theionization of nitrogen molecules and reduces the recombinationprobability of N⁺, N₂ ⁺, N₃ ⁺, and N₄ ⁺ ions. The mixture of nitrogenand helium is preferred over the use of nitrogen alone, since the heliumbased plasma's ions are able to enhance ionization efficiency, therebypromoting ion reactivity and achieving greater penetration depths. Thegreater penetration depths provide for the displacement of a greateramount of hydrogen, so that the reduction of the deposited material'sresistivity may be maximized. Further, helium's small mass enables it tofill vacancies that are left in the deposited material by exitinghydrogen atoms which are too small to be filled by the nitrogen ions.

In accordance with the present invention, a wafer 114 is placed in achamber, such as chamber 110A, and a layer of material is deposited onthe wafer, as described above. The deposited material may be titaniumnitride for use as a diffusion barrier.

Once the layer of material is deposited, it undergoes a first annealingprocess of ion bombardment. While residing on the wafer support 116, thewafer 114 may be about 0.3 to 0.8 inches from the showerhead 136.Preferably, the wafer 114 is between 0.6 and 0.7 inches from theshowerhead 136.

The ion bombardment is achieved by first transferring a gas into theprocessing chamber 112 via the showerhead 136. In one embodiment of thepresent invention, the gas is a mixture of nitrogen and hydrogen havinga 2:3 nitrogen to hydrogen ratio and being introduced into theprocessing chamber 112 with a nitrogen flow rate of approximately 600sccm. The pressure in the processing chamber 112 is set to approximately1.0 Torr., and the wafer temperature is set to be between 350-450° C. Inan alternative embodiment of the present invention, the gas may becomprised of a mixture having a nitrogen to hydrogen ratio between 3:1and 1:2.

Next in the first annealing process, the rf source 142 supplies a rfsignal to the showerhead 136 and the wafer support 116. This causes thegas to form a plasma containing positively charged ions. The rf source142 may supply 350 watts of rf power at 350 kHz, through the matchingnetwork 145, to produce rf signals to the showerhead 136 and wafersupport 116 that are 180 degrees out of phase. Typically, the plasma ismaintained for 20 seconds. The rf source 142 may alternatively supply350 watts of rf power at a frequency below 1 MHz.

The repeated cycling of voltage from the rf source 142 results in asurplus of electrons in the vicinity of the wafer 114 that produces anegative bias at the wafer 114. The wafer support 116 may acquire anegative bias between -100 to -400 volts, typically -300 volts, whilethe showerhead 136 may acquire a negative bias between -100 to -400volts, typically -200 volts. The processing chamber 112 is grounded, andthe negative bias of the wafer 114 is between -100 to -400 volts,typically -300 volts, which remains approximately constant during theperiod of ion bombardment.

During the ion bombardment, the positively charged ions from the plasmaare accelerated by the voltage gradient into the surface of the wafer114 and penetrate the surface of the wafer to a depth between 100 to 110Å. Energetic neutral atomic particles from the plasma may also bombardthe wafer 114. Once the 20 seconds of the first annealing is completed,the processing chamber 112 is purged.

Next, the second annealing process is initiated. In one embodiment ofthe present invention, the plasma generating gas is only nitrogen. Thegas is introduced into the processing chamber 112 with a nitrogen flowrate of approximately 500-1000 sccm. The pressure in the processingchamber 112 is set to approximately 1.0 Torr., and the wafer temperatureis set to be between 350-450° C.

In an alternative embodiment of the present invention, the gas may amixture of nitrogen and helium with a nitrogen to helium ratio between0.2 and 1.0. Gases containing other combinations of nitrogen and eitherargon, neon, helium or combinations thereof may also be used.

Next in the second annealing process, the rf source 142 supplies a rfsignal to the showerhead 136 and the wafer support 116. This causes thegas to form a plasma containing positively charged ions. The rf source142 may supply 300-1,500 watts of rf power at 300-400 KHz, through thematching network 145, to produce rf signals to the showerhead 136 andwafer support 116 that are 180 degrees out of phase. Typically, theplasma is maintained for 15 seconds. The rf source 142 may alternativelysupply 300-1,500 watts of rf power at a different frequency below 13.56MHz. The power of the source is scaleable based on the need forprocessing different size wafers.

As in the case of the first annealing, the repeated cycling of voltagefrom the rf source 142 results in a surplus of electrons in the vicinityof the wafer 114 that produces a negative bias at the wafer 114. Thewafer support 116 may acquire a negative bias between -100 to -400volts, typically -300 volts, while the showerhead 136 may acquire anegative bias between -100 to -400 volts, typically -200 volts. Theprocessing chamber 112 is grounded, and the negative bias of the wafer114 is between -100 to -400 volts, typically -300 volts, which remainsapproximately constant during a period of ion bombardment.

During the second ion bombardment, the positively charged ions from theplasma are accelerated by the voltage gradient into the surface of thewafer 114. The ions penetrate the surface of the wafer 114 to displacethe hydrogen molecules in the deposited and annealed material. Energeticneutral atomic particles from the plasma may also bombard the wafer 114.Once 15 seconds of the second annealing is completed, the processingchamber is purged.

When a nitrogen gas is employed, the ions penetrate to a depth between70 to 80 Å. When the gas is a mixture of nitrogen and helium, the ionspenetrate to a depth between 100 to 125 Å. Accordingly, the annealingwith the mixture of nitrogen and helium provides for the displacement ofmore hydrogen molecules than the annealing that only employs nitrogen.

In order to form a diffusion barrier having a desirable thickness, suchas between 150 to 300 Å, the above described CVD deposition andsequential annealing processes are repeated. Layers of barrier materialbetween 50 to 100 Å thick are successively deposited and sequentiallyannealed, until the desired film thickness is achieved.

When the sequential annealing process is performed in either chamber110A, chamber 110B, or chamber 110C, the deposition, first annealing,and second annealing may all be performed in the same chamber.Accordingly, the deposition and sequential annealing may be performedin-situ. However, the process steps of deposition and sequentialannealing are not required to be performed in-situ and alternativechambers may be employed.

Table VI, which appears in FIG. 42, reflects experimental results thatwere obtained to compare the sequential annealing process with thesingle annealing process. In order to collect the data in Table VI, aset of wafers were each processed in accordance with differentembodiments of the present invention. A 200 Å thick layer of titaniumnitride was formed on each wafer in accordance with the presentinvention.

A first wafer was processed in accordance with the single annealingprocess described above using a gas of nitrogen and hydrogen to generatethe annealing plasma. A second wafer was processed using sequentialannealing with a plasma gas including only nitrogen. A third wafer wasprocessed using sequential annealing with a plasma gas includingnitrogen and helium. A fourth wafer was processed using a three phasesequential annealing with 15 seconds of a nitrogen-hydrogen plasmaannealing, 15 seconds of a nitrogen plasma annealing, and 5 seconds of anitrogen-hydrogen plasma annealing, in that order.

The second wafer, which employed the sequential annealing with nitrogengas, showed significantly less resistivity than the first wafer whichonly underwent a single annealing step. The second wafers resistivitywas between 450-500 Ω-cm, while the first wafers resistivity was between570-630 Ω-cm. Further, the second wafers increase in resistivity after50 hours was only 7-8%, while the first wafers increase was between11-12%.

Even better results were seen in the third wafer, which employed amixture of nitrogen and helium in the second plasma annealing. The thirdwafer had a resistivity between 440-480 Ω-cm, which only increased by3-7% over a 50 hour time period. The third wafer also had a smallerconcentration of oxygen. The lower levels of oxygen in the third wafer,as compared to the second wafer, may be credited to the nitrogen-heliummixtures superior ability to remove hydrogen from the titanium nitridelayer.

The fourth wafer, which underwent a third annealing using a mixture ofnitrogen and hydrogen had resistivity and resistivity aging measurementsclose to those of the first wafer. This shows that the reintroduction ofhydrogen to the titanium nitride layer after the second annealingcreates a surplus of hydrogen. The surplus of hydrogen negates thebenefits achieved in the second annealing.

4. Oxidation to Reduce Diffusivity

In addition to providing a film on a wafer with improved resistivity,the following process enables the film to better impede the diffusion ofcontact metals into a substrate underlying the film. In particular, thefilm will be treated to better impede the diffusion of aluminum.

First, a layer of material is formed on an upper surface of a wafer 114in-situ (i.e. without the wafer being removed from a processing chamber112 at anytime during the layers formation). In one embodiment of thepresent invention, a deposition and subsequent plasma annealing of thematerial is performed in chamber 110A to form the film. The layer ofmaterial may be deposited on the upper surface of the wafer 114 using athermal CVD process, so that the material conforms to the upper surfaceof the wafer 114. During the deposition, the pressure control unit 157may set the pressure in the processing chamber between 0.6 to 1.2 Torr,and the lamps 130 may set the temperature of the wafer 114 to be between360 to 380° C.

In one embodiment of the present invention, the deposited material maybe a barrier material, such as a binary metal nitride, like titaniumnitride (TiN) or tantalum nitride (TaN). In an alternative embodiment ofthe present invention, a ternary metal silicon nitride may be used asthe barrier material instead of a binary metal nitride. The depositedmaterial may have a thickness of between 50 and 300 Å, preferably beingbetween 50 and 100 Å.

Once the layer of barrier material is deposited, it is annealed througha process of ion bombardment. While residing on the wafer support 116,the wafer 114 may be about 0.3 to 0.8 inches from the showerhead 136.Preferably, the wafer 114 is between 0.6 and 0.7 inches from theshowerhead 136.

The ion bombardment is achieved by first transferring a gas into theprocessing chamber 112 via the showerhead 136. In one embodiment of thepresent invention, the gas is a mixture of nitrogen and hydrogen havinga 2:3 nitrogen to hydrogen ratio and being introduced into theprocessing chamber 112 with a nitrogen flow rate of approximately 400sccm. The pressure in the processing chamber 112 is set to approximately1.0 Torr., and the wafer temperature is set to be between 300 and 400°C., and preferably is 360° C.

In an alternative embodiment of the present invention, the gas may becomprised of a gas having a nitrogen to hydrogen ratio between 3:1 and1:2. Gases containing other combinations of nitrogen, hydrogen, andeither argon, helium or ammonia may also be used.

Next in the annealing process, the rf source 142 supplies a rf signal tothe showerhead 136 and the wafer support 116 causing the gas 206 to forma plasma 207 containing positively charged ions. The rf source 142 maysupply 350 watts of rf power at 350 KHz, through the matching network145, to produce rf signals to the showerhead 136 and wafer support 116that are 180 degrees out of phase. Typically, the plasma is maintainedfor 10 to 30 seconds. The rf source 142 may alternatively supply 350watts of rf power at a different frequency below 1 MHz.

A negative bias is produced at the wafer 114. The wafer support 116 mayacquire a negative bias between -100 to -400 volts, typically -300volts, while the showerhead 136 may acquire a negative bias between -100to -400 volts, typically -200 volts. The processing chamber 112 isgrounded, and the negative bias of the wafer 114 is between -100 to -400volts, typically -300 volts, which remains approximately constant duringthe period of ion bombardment.

During the ion bombardment, the positively charged ions from the plasmaare accelerated by the voltage gradient into the surface of the wafer114 and penetrate the surface of the wafer to a depth between 50 to 200Å. Energetic neutral atomic particles from the plasma 207 may alsobombard the wafer 114.

The ion bombardment causes the thickness of the deposited layer ofbarrier material to be reduced by 20% to 50% depending on thetemperature of the substrate and the plasma treatment time and energy.As described above, the CVD deposition and annealing processes may berepeated using layers of barrier material between 50 to 100 Å thick toform a layer of material with a desired thickness.

Alternatively, the deposition and annealing of the material on the wafer114 may be carried out by a number of different means. U.S. patentapplication Ser. No. 08/339,521, entitled IMPROVED TITANIUM NITRIDELAYERS DEPOSITED BY CHEMICAL VAPOR DEPOSITION AND METHOD OF MAKING, U.S.patent application Ser. No. 08/498,990, entitled BIASED PLASMA ANNEALINGOF THIN FILMS, U.S. patent application Ser. No. 08/567,461, entitledPLASMA ANNEALING OF THIN FILMS, and U.S. patent application Ser. No.08/680,913, entitled PLASMA BOMBARDING OF THIN FILMS, each disclose aprocess for forming a layer of barrier material on an upper surface of awafer through the use of a CVD process and plasma annealing. Each ofthese applications is hereby incorporated by reference. Each of theprocesses disclosed by these applications may be employed in embodimentsof the present invention to form a layer of material on a wafer.

In one embodiment of the present invention, the wafer is placed in anapparatus that can perform physical vapor deposition, and the layer ofmaterial is formed by a conventional sputtering process. In analternative embodiment of the present invention, the wafer is placed ina chamber that can perform chemical vapor deposition, and the layer ofmaterial is formed through a CVD process, without additional plasmaannealing.

In the manufacture of integrated circuits, aluminum is frequentlyemployed as a contact metal. Since aluminum has an affinity for oxygen,the diffusivity of aluminum may be reduced in oxygen rich materials.Therefore, the layer of material formed on the wafer 114 can beprocessed to act as an enhanced diffusion barrier to an aluminum contactmetal by infusing the material with oxygen.

In order to infuse the material with oxygen, the material on the wafer114 is oxidized in-situ (i.e. without being removed from the processingchamber 112 after the layer of material is formed, until the oxidationis completed). Hence, the entire process of forming the layer ofmaterial and oxidizing the layer of material may be performed in-situ ina single chamber. The oxidation is performed so that the grainboundaries of the material become oxidized, while the material's grainsthemselves experience very little oxidation.

The oxidation of the material's grain boundaries may be achieved in-situthrough the use of the semiconductor wafer processing chamber 110A shownin FIG. 5. Once the layer of material is formed (deposited and annealed)on the wafer 114, the wafer 114 remains in the processing chamber 112.The pressure control unit 157 sets the pressure in the processingchamber 112 to be between 0.5 and 1.0 Torr. The wafer 114 temperature isset to be between 300 and 400° C., and is preferably 360° C.

The layer of material is exposed to an oxygen bearing gas, such as a N₂/O₂ mixture or O₂. The gas is transferred into the processing chamber112 through the showerhead 136 at a flow rate between 100-1000 sccm. Thegas 208 may include both nitrogen and oxygen and have a mixture ratio ofnitrogen to oxygen of 4:1. Next, the rf source 142 supplies a signalthrough the matching network 145 to both the wafer support 116 and theshowerhead 136 to convert the gas into a plasma containing positivelycharged oxygen ions.

The rf source 142 supplies 350 watts of rf power at 350 KHz through thematching network 145 for approximately 20 seconds to produce rf signalsat the showerhead 136 and the wafer support 116 that are 180 degrees outof phase. The showerhead 136, wafer support 116 and wafer 114 eachacquire a negative bias, as described above for the annealing process.As a result, the positively charged oxygen ions accelerate toward thewafer 114 and penetrate the surface of the layer of material and attachto the grain boundaries of the material.

Once this oxidation is completed in one embodiment of the presentinvention, the oxidized layer of material is oxidized titanium nitride.The oxidized titanium nitride is able to operate as an enhanceddiffusion barrier to contact metals that have an affinity for oxygen,such as aluminum. Alternatively, an enhanced diffusion barrier may alsobe formed in accordance with the present invention, when the layer ofmaterial is another binary metal nitride M_(x) N_(y) or a ternary metalsilicon nitride M_(x) Si_(y) N_(z), (where M may be Ti, Zr, Hf, Ta, Mo,W and other metals).

In an alternative embodiment of the present invention, the samesemiconductor wafer processing chamber 110A is employed to perform athermal oxidation of the material. An oxygen bearing gas, such asoxygen, ozone, air or water, is transferred into the processing chamber112 via the showerhead 136 at a flow rate between 100 and 1000 sccm. Thelamps 130 then heat the wafer 114 to a temperature between 300 and 400°C., while the pressure in the processing chamber is set to be between0.5 and 1000 Torr., and is preferably 1.0 Torr.

As a result, oxygen in the oxygen bearing gas penetrates the surface ofthe layer of barrier material and attaches to the grain boundaries ofthe barrier material. One process for oxidizing a barrier material'sgrain boundaries is disclosed in U.S. Pat. No. 5,378,660, entitledBARRIER LAYERS AND ALUMINUM CONTACTS, issued to Ngan, et al., and herebyincorporated by reference. Once the layer of material 200 is formed andoxidized, the wafer 114 is removed from the processing chamber 112.

Although the formation and oxidation of the layer of material on thewafer 114 has been specifically described to be performed in thesemiconductor wafer processing chamber 110A in FIG. 5, the process isnot restricted to being performed in chamber 110A. The process may alsobe carried out in any semiconductor wafer processing chamber thatprovides for carrying out the in-situ formation and oxidation processingin accordance with the present invention, such as the chambers 110B and110C depicted in FIGS. 16 and 17, respectively.

Traditionally, diffusion barriers have been made thicker to providegreater protection against the diffusion of contact metals. As a resultof embodiments of the present invention, diffusion barriers do not haveto be made thicker to inhibit the diffusion of contact metals. Inembodiments of the present invention, the oxidation of the barriermaterial reduces the diffusivity of contact metals with an affinity foroxygen, such as aluminum. As such contact metals begin to diffuse intoan oxidized layer of barrier material, such as titanium nitride, thecontact metals bond with the oxygen ions that are attached to the grainboundaries of the barrier material. As a result, the contact metals areunable to reach the region underlying the diffusion barrier.

The chart in FIG. 43(a) shows the chemical composition at differentdepths of a wafer, after a layer of barrier material has been depositedand plasma annealed in accordance with the present invention, but notoxidized. FIG. 43(b) includes a chart that shows the chemicalcomposition at different depths of a wafer, after a layer of barriermaterial has been deposited, plasma annealed, and oxidized in accordancewith the present invention.

Each of these charts represents data that was taken from a wafer havinga silicon substrate overlaid by a barrier layer of titanium nitride. Thewafer was probed by Auger electron spectroscopy. Each chart shows theatomic concentration of different chemicals in the wafer at differentdepths of the wafer. As can be seen by comparing the two charts, theoxygen level in the top portion of the wafer, which constitutes thebarrier material, is significantly higher in the oxidized barriermaterial (FIG. 43(b)) than in the non-oxidized barrier material (FIG.43(a)).

The presence of the oxygen in the barrier material causes a contactmetal, such as aluminum, to have its diffusivity greatly decreased, bybonding with the oxygen ions in the barrier material. Accordingly, theoxidized barrier material (FIG. 43(b)) provides a better diffusionbarrier between a contact metal, such as aluminum, and an underlyingsilicon substrate than does the non-oxidized barrier material (FIG.43(a)).

Additionally, the sheet resistance of diffusion barriers formed byembodiments of the present invention are not unacceptably compromised bythe oxidation process. FIG. 44 shows a table that illustrates this fact.As shown in the table, a 200 Å layer of titanium nitride barriermaterial, which is deposited and plasma annealed in accordance with thepresent invention, but not oxidized, may have a sheet resistance of 410Ω/sq. and a sheet resistance uniformity standard deviation of 2.2%. Theresulting resistivity of such a layer of barrier material is 820 Ω-cm. A200 Å layer of titanium nitride barrier material, which is deposited,plasma annealed, and oxidized for 20 seconds in accordance with thepresent invention, may have a sheet resistance of only 630 Ω/sq. and asheet resistance uniformity standard deviation of 3.7%. The resultingresistivity of such a layer of barrier material is 1260-cm.

The table in FIG. 44 also shows the sheet resistance for a 300 Å layerof titanium nitride barrier material. After being deposited and plasmaannealed in accordance with the present invention, the 300 Å layer oftitanium nitride barrier material may have a sheet resistance of 235Ω/sq. and a sheet resistance uniformity standard deviation of 2.0%.After deposition, plasma annealing, and oxidation for 20 seconds inaccordance with the present invention, the 300 Å layer of titaniumnitride barrier material may have a sheet resistance of 250 Ω/sq. and asheet resistance uniformity standard deviation of 2.7%. Accordingly, thenon-oxidized 300 Å layer of barrier material may have a resistivity of705 Ω-cm, while the oxidized 300 Å layer of barrier material may have aresistivity of only 750-cm.

The relative effectiveness of the non-oxidized and oxidized layers oftitanium nitride barrier material that appear in the table in FIG. 44were evaluated as follows. A 1,000 Å layer of aluminum was deposited onwafers having upper surfaces comprised of either the non-oxidized or theoxidized layers of titanium nitride barrier material. After beingdeposited on the wafers, the aluminum was annealed in a furnace for onehour at 550° C. Wafers having the 200 Å and 300 Å layers of titaniumnitride barrier material, which was not oxidized, experienced severedefects from diffusion of the aluminum into the wafer's substrate.Wafers having the 200 Å and 300 Å layers of titanium nitride barriermaterial, which was deposited, plasma annealed and oxidized inaccordance with the present invention, suffered only minor defects or nodefects, respectively, from the diffusion of aluminum.

The data in FIGS. 43(a), 43(b) and 44 is only one possible set ofresults that can be achieved from practicing embodiments of the presentinvention. The results set forth in these figures are in no way meant tolimit embodiments of the present invention to achieving the same orsubstantially the same results.

5. Silicon Enrichment to Reduce Diffusivity

In another embodiment of the present invention, the oxidation step isreplaced by a silicon stuffing procedure. The silicon stuffing procedurereduces the diffusivity of contact metals, such as copper, in a layer(film) of material, such as titanium nitride or tantalum nitride,overlying a substrate. The ability of silicon to bond with nitrogen tofill grain boundaries of deposited material is the mechanism thatpromotes the enhancement of the films barrier properties.

In accordance with the present invention, a deposition and annealing ofa material, such as titanium nitride or tantalum nitride, on a wafer isperformed in the same manner as described above for the processincluding an oxidation step. Preferably, a 100 Å film of titaniumnitride or tantalum nitride is deposited. After annealing the materialwith a plasma that includes a mixture of nitrogen and hydrogen, thethickness of the film is approximately 50IÅ.

The deposition and annealing of the film material may be performed inany one of chambers 110A, 110B, or 110C. Alternatively, another chamberor set of chambers capable of performing the deposition and annealingsteps may be employed. If either chamber 110A, 110B, or 110C isemployed, the silicon stuffing may be performed in the same chamber asthe deposition and annealing. As a result, the entire silicon stuffingprocess may be performed in-situ.

After the deposition and annealing, silicon stuffing is performed byexposing the annealed film to silane (SiH₄). Silane is flowed into theprocessing chamber 110A at a rate of 30 sccm for approximately 30seconds. During the silane exposure, the chamber pressure is set to 1.2Torr; the wafer support 116 is heated to a temperature of 420° C., andnitrogen is flowed into the chamber 110A at a rate of 140 sccm. An argonpurge flow of 200 sccm is employed. The exposure to silane is followedby an exhaustive purge to sweep the residual SiH₄ from the chamber 110Aand delivery lines.

During the exposure, the silicon bonds with the titanium nitride ortantalum nitride at the surface of the film to fill the grain boundariesin the deposited material. The stuffed silicon will impede the diffusionof later deposited contact metals, such as copper.

The steps of depositing, annealing, and silicon stuffing the filmmaterial are repeated successively until the film being constructed hasa desired thickness. In constructing a 200 Å film, the depositing,annealing, and exposure of the film material is preferably performed atotal of three times, with a 100 Å layer of titanium nitride or tantalumnitride being deposited each time. As a result, a silicon stuffed filmhaving a thickness of 150 Å is built. In order to reach the desiredthickness of 200 Å, a final 100 Å cap layer of titanium nitride ortantalum nitride is deposited and annealed to a thickness of 50 Å. Thecap layer material may be annealed using a plasma containing bothnitrogen and/or hydrogen, as described above. This final deposited andannealed cap layer of material is not exposed to silane.

The final section of material that is deposited and annealed is notexposed to silane because of silanes affinity for oxygen. If siliconwere introduced into the final surface cap of the titanium nitride filmthrough exposure to silane, the resistivity of the film may becomeunacceptably high. After capping the film with an annealed layer of, forexample, titanium nitride, the resistivity of the film is approximately520 Ω-cm. If the top layer of the film was exposed to silane, theresistivity of the film could possibly be much higher.

Rutherford backscattering spectroscopy revealed that a titanium nitridefilm stuffed with silicon in conformance with the present invention hadthe following profile: Si content of 5 atomic percent, Ti content of35.2 atomic percent, N content of 52.8 atomic percent and H content of 7atomic percent. An Auger depth profile of the film formed in accordancewith the present invention is shown in FIG. 45. The Auger depth profileshows a uniform nitrogen and titanium content with an oscillatingsilicon content that is in line with the 150 Å of silicon containingmaterial being capped by titanium nitride.

It should be noted that the above measurements and procedures areprovided as a non-limiting example of how silicon stuffing may beperformed in accordance with the present invention. In an alternateembodiment of the present invention, the steps of annealing the layer ofmaterial deposited on the substrate and exposing the material to silanemay be interchanged. As a result, the deposited material, such astitanium nitride, would first be exposed to silane for the purpose ofsilicon stuffing and then be annealed using a plasma to reduce thematerials resistivity. Additionally, deposition processes other thanchemical vapor deposition, such as sputtering, may be employed.

As an alternative to silicon stuffing, a ternary metal silicon nitridematerial, such as titania silica carbo nitride (TiSiCN), may bedeposited instead of a titanium nitride material. The deposited siliconrich material would then be annealed to reduce its resistivity. As inthe above described processes, the deposition and annealing could beperformed repeatedly to form a film having a desired thickness.

In accordance with such an embodiment of the present invention, a waferis placed in a chamber that is capable of performing a depositionprocess. The chamber may be either chamber 110A, 110B, or 110C, whichenable the silicon rich film to be constructed in-situ. Alternatively, adifferent chamber or set of chambers may be employed to carry out thefollowing steps of forming the silicon rich film.

Once the wafer is placed in a chamber, a titania silica carbo nitride(TiSiCN) material is deposited on the wafer. The deposition may beperformed using conventional thermal CVD employing TDMAT. In order tointroduce the silicon, a volume of silane is flowed into the chamber. Anequal volume of nitrogen dilutant is withheld, as compared to the volumeused when depositing titanium nitride using CVD with TDMAT.

In performing the deposition, the chamber pressure is set to 1.2 Torr;the wafer support temperature is set to 420° C., and silane, He/TDMAT,and nitrogen dilutant are flowed into the chamber with the flow rates of10 sccm, 70 sccm, and 90 sccm, respectively. An argon purge is performedat a flow rate of 200 sccm. The deposition may be performed for 32seconds to form a layer of material that is 100 Å thick. In the chemicalvapor deposition of titanium nitride, no silane would have been employedand the nitrogen flow rate would have been 100 sccm.

The deposition is followed by the annealing of the TiSiCN with a plasmaof nitrogen and hydrogen, as described above for the process includingoxygen stuffing. The annealing includes an ion bombardment that takesplace for 20 seconds when the deposited material has a beginningthickness of 100 Å and a 50IÅ thick layer of material is desired. Thedeposition and annealing may be repeated successively to construct afilm having a desired thickness. In one embodiment of the presentinvention, a 200 Å film is desired. A 100 Å layer of TiSiCN is depositedand then annealed to become a 50 Å layer of material. The 100 Ådeposition and annealing of TiSiCN is performed a total of four times toobtain the desired 200 Å film.

In one instance, Rutherford backscattering spectroscopy showed that theresulting 200 Å film contained 15 atomic percent Si, 25.3 atomic percentTi, 49.7 atomic percent N, and 10 atomic percent H. Auger depth profileof the film is shown in FIG. 46. The Auger depth profile shows a uniformcomposition with a low carbon content of approximately 5 atomic percentand an oxygen content of 1 atomic percent. The resistivity of the filmis 2,400 Ω-cm. FIG. 47 shows a comparison of the resistivity andcomposition of the 200 Å film that is formed using silicon stuffing andthe 200 Å film that is formed by depositing titania silica carbonitride.

The high resistivity is a trade-off that is incurred for obtaining avery silicon rich film to operate as a diffusion barrier. A resistivityof 1,000 Ω-cm is more acceptable for a diffusion barrier. The amount ofsilane used in the deposition step may be reduced to lower the filmsresistivity. The best resistivity is achieved by stuffing the siliconinto a layer of material after deposition and annealing, as describedabove. However, a silicon stuffed diffusion barrier does not provide asstrong a deterrent to the diffusion of copper as a film that isconstructed by depositing a silicon containing material. For example, asilicon stuffed binary metal nitride, such as titanium nitride, does notprevent the diffusion of copper as well as a film constructed bydepositing a ternary metal silicon nitride, such as TiSiCN. Anintegrated circuit manufacturer may select the method of siliconenrichment that best meets the manufacturers needs in constructing afilm.

It should also be noted that the deposition process employed in each ofthe above described silicon enrichment procedures may be varied. Inplace of chemical vapor deposition, other deposition processes, such assputtering, may be employed. Ternary metal silicon nitride other thanTiSiCN may also be used in embodiments of the present invention.

Further, the annealing steps described above are not restricted to usingplasmas consisting only of nitrogen and hydrogen. Other plasmacompositions which serve to lower the resistivity of a depositedmaterial may be used. An example of such a plasma is the one describedabove containing nitrogen, hydrogen, and argon. Sequential annealing mayalso be employed.

In the process including silicon stuffing by exposure to silane, theexposure step is not limited to being thermally energized. Inalternative embodiments of the present invention, a plasma containingsilicon ions may be generated by an rf signal energizing a silicon richgas. A wafer containing the material to be silicon stuffed may also bebiased to enhance the impact of the silicon into the material. Whenperforming silicon stuffing using plasma, the silicon stuffing may alsobe performed either before or after the step of annealing the materialto reduce its resistivity.

C. Processor Controlled Film Construction

The above-described process steps of depositing, annealing, oxidizing,and silicon stuffing a material may be performed in a chamber that iscontrolled by a processor based control unit. FIG. 48 shows a controlunit 600 that may be employed in such a capacity. The control unitincludes a processor unit 605, a memory 610, a mass storage device 620,an input control unit 670, and a display unit 650 which are all coupledto a control unit bus 625.

The processor unit 605 may be a microprocessor or other engine that iscapable of executing instructions stored in a memory. The memory 610 maybe comprised of a hard disk drive, random access memory ("RAM"), readonly memory ("ROM"), a combination of RAM and ROM, or other memory. Thememory 610 contains instructions that the processor unit 605 executes tofacilitate the performance of the above mentioned process steps. Theinstructions in the memory 610 may be in the form of program code. Theprogram code may conform to any one of a number of different programminglanguages. For example, the program code may be written in C+, C++,BASIC, Pascal, or a number of other languages.

The mass storage device 620 stores data and instructions and retrievesdata and instructions from a processor readable storage medium, such asa magnetic disk or magnetic tape. For example, the mass storage device620 may be a hard disk drive, floppy disk drive, tape drive, or opticaldisk drive. The mass storage device 620 stores and retrieves theinstructions in response to directions that it receives from theprocessor unit 605. Data and instructions that are stored and retrievedby the mass storage device 620 are employed by the processor unit 605for performing the above mentioned process steps. The data andinstructions may first be retrieved by the mass storage device 620 froma medium and then transferred to the memory 610 for use by the processorunit 605.

The display unit 650 provides information to a chamber operator in theform of graphical displays and alphanumeric characters under control ofthe processor unit 605. The input control unit 670 couples a data inputdevice, such as a keyboard, mouse, or light pen, to the control unit 600to provide for the receipt of a chamber operators inputs.

The control unit bus 625 provides for the transfer of data and controlsignals between all of the devices that are coupled to the control unitbus 625. Although the control unit bus is displayed as a single bus thatdirectly connects the devices in the control unit 600, the control unitbus 625 may be a collection of busses. For example, the display unit650, input control unit 670 and mass storage device 620 may be coupledto an input-output peripheral bus, while the processor unit 605 andmemory 610 are coupled to a local processor bus. The local processor busand input-output peripheral bus may be coupled together to form thecontrol unit bus 625.

The control unit 600 is coupled to the elements of a chamber that areemployed to form a film on a substrate. Each of these elements may becoupled to the control unit bus 625 to facilitate communication betweenthe control unit 600 and the element. These elements include the gaspanel 52, heating elements, such as lamps 130, pressure control unit157, rf source or sources 62, 142, 143, 144, and temperaturedetermination device 140 of the chamber. In one embodiment of theinvention, the control unit 600 is the gas panel controller 50 calledfor in chambers 110A, 110B, and 110C. The control unit 600 providessignals to the elements that cause the elements to perform theoperations described above for the process steps of depositing,annealing, oxidizing, and silicon stuffing material on a substrate. Thecontrol unit 600 may also receive signals from these elements todetermine how to proceed in controlling the execution of theaforementioned process steps. For example, the control unit 600 receivessignals from the temperature determination device 140 to determine theamount of heat that the lamps 130 should provide to the chamber.

FIG. 49 illustrates a sequence of process steps that may be performed bythe processor unit 605 in response to the program code instructions thatit retrieves from the memory 610. Upon initiating the formation of afilm on a substrate, a deposition step 700 is performed. In thedeposition step 700, the processor unit 605 executes instructionsretrieved from the memory 610. The execution of these instructionsresults in the elements of the chamber being operated to deposit a layerof material on a substrate as described above. For example, theprocessor unit 605, in response to the retrieved instructions, causesthe gas panel to provide precursor gases in the chamber, the lamps 130to heat the chamber, and the pressure control unit 157 to set thepressure in the chamber.

Once the deposition step 700 is completed, instructions retrieved fromthe memory 610 instruct the processor unit 605 to cause the elements ofthe chamber to perform an annealing step 701, such as one of the abovedescribed annealing procedures. The annealing may include plasmaannealing with either nitrogen, hydrogen, a mixture of nitrogen andhydrogen, or a mixture of nitrogen, hydrogen, and another gas such asargon. Alternatively, the annealing step 701 may cause a sequentialannealing to be executed as described above.

After completing the annealing step 701, an oxidation determination step702 is performed in which the control unit 600 determines whether anoxidation process step is to be executed. If no oxidation is to beperformed, instructions are retrieved from the memory 610 in step 703 tocause the processor unit 605 to determine whether silicon stuffing is tobe performed. If no silicon stuffing is to be performed, the controlunit 600 determines whether another deposition is to be performed instep 706. A deposition is performed, unless the already depositedmaterial has a thickness substantially equal to a desired filmthickness. If the desired film thickness has been reached, the processof constructing a film on a substrate is complete. Otherwise, a newdeposition step 700 is performed.

If it is determined in the oxidation determination step 702 that anoxidation is to be performed, then the processor unit 605 executes anoxidation step 704. In the oxidation step 704, the retrievedinstructions cause the processor unit 605 to instruct the elements ofthe chamber to perform the operations necessary to carry out the abovedescribed process step of oxidizing the deposited material. Theoxidation may be either plasma based or thermal. Upon completion of theoxidation step 704, the processor unit 605 determines whether a newdeposition step 700 should be performed in step 706.

If it is determined in step 703 that silicon stuffing is to beperformed, then the processor unit 605 executes a silicon stuffing step705. The processor unit 605 retrieves and executes silicon stuffinginstructions in the memory 610. In response to these instruction, theprocessor unit 605 causes the elements of the chamber to operate in amanner that enables the above described silicon stuffing procedure to beexecuted. The silicon stuffing may be achieved through an exposure ofthe deposited material to a silane gas that is thermally infused withenergy. Alternatively, the silicon stuffing may be achieved by exposingthe deposited material to an environment containing silicon ions thatare created by generating a plasma using an rf signal. Upon completionof the silicon stuffing step 705, the deposition step 700 is repeated.

FIG. 50 illustrates an alternate sequence of process steps that may beperformed by the processor unit 605 in response to the program codeinstructions that it retrieves from the memory 610. This sequence ofprocess steps includes the same steps as shown in FIG. 49. However, theorder of the steps is altered to provide for performing the siliconstuffing step 705 prior to the annealing step 701.

Immediately after the deposition step 700 is performed, the processorunit 605 executes instructions in step 703 to determine whether siliconstuffing is to be performed. If it is, then the silicon stuffing step705 is performed and followed by the annealing step 701. Otherwise, theannealing step 701 is performed. After the annealing step 701, theprocessor unit 605 determines in step 702 whether oxidation is to beperformed. If it is, then the oxidation step 704 is executed. Otherwise,a determination is made, in step 706, whether to perform a newdeposition. The determination in step 706 is also made once theoxidation step 704 is completed. If a new deposition is required, thedeposition step 700 is executed. Otherwise, the film constructionprocess is completed.

Although the present invention has been described in terms of specificexemplary embodiments, it will be appreciated that various modificationsand alterations might be made by those skilled in the art withoutdeparting from the spirit and scope of the invention as specified in thefollowing claims.

What is claimed is:
 1. A method for constructing a tantalum nitride filmon a semiconductor wafer, said method comprising:(a) depositing a layerof tantalum nitride material on said wafer; and (b) following said step(a), plasma annealing said layer of tantalum nitride material.
 2. Themethod of claim 1, wherein said step (b) includes the steps of:exposingsaid layer of tantalum nitride material to an environment containingions.
 3. The method of claim 2, wherein said step (b) includes the stepsof:electrically biasing said layer of tantalum nitride material to causesaid ions from said environment to impact said layer of tantalum nitridematerial.
 4. The method of claim 2, wherein said step of exposing saidlayer of tantalum nitride material to said environment containing ionsincludes the steps of:providing a gas; and providing energy to said gas.5. The method of claim 4 wherein said energy is provided by an RF sourcehaving an output power of greater than approximately 350 watts.
 6. Themethod of claim 4 wherein said energy is provided by an RF source havingan output power of approximately 900 watts.
 7. The method of claim 3,wherein said step of providing energy to said gas includes the stepof:providing a first rf signal to a first electrode on a first side ofsaid wafer.
 8. The method of claim 4, wherein said step of providingenergy to said gas further includes the step of:providing a second rfsignal to a second electrode on a second side of said wafer.
 9. Themethod of claim 6, wherein said first rf signal is substantially 180degrees out of phase with said second rf signal.
 10. The method of claim4, wherein said gas contains at least one gas selected from the groupconsisting of nitrogen, hydrogen, argon, helium, and ammonia.
 11. Themethod of claim 4 wherein said gas is hydrogenIH₂.
 12. The method ofclaim 1, wherein said step (a) and said step (b) are both performed in asingle chamber and without removing the wafer from the chamber betweenbeginning said step (a) and completion of said step (b).
 13. The methodof claim 1, wherein said step (a) is performed using chemical vapordeposition.
 14. The method of claim 11, wherein said layer of tantalumnitride material is deposited by thermal decomposition of at least onemetallo-organic tantalum compound.
 15. The method of claim 14 whereinsaid at least one metallo-organic tantalum compound is formed using amixture of ethyliminoethyl(C,N)tris(diethylamido)tantalum andethylimidotris(diethylamido)tantalum.
 16. The method of claim 1, furtherincluding the step of:(c) repeating said step (a) and said step (b). 17.The method of claim 16 wherein step (a) is performed until approximately25 angstroms of tantalum nitride is deposited with each execution ofstep (a).
 18. The method of claim 1, further including the step of:(c)oxidizing said layer of tantalum nitride material following said step(b).
 19. The method of said step 18, wherein said step (a), said step(b), and said step (c) are all performed in a single chamber.
 20. Themethod of claim 18, wherein said step (c) includes the steps of:exposingsaid layer of tantalum nitride material to an environment containingoxygen ions; and electrically biasing said layer of tantalum nitridematerial to cause said oxygen ions from said environment to impact saidlayer of tantalum nitride material.
 21. The method of claim 20, whereinsaid step of exposing said layer of tantalum nitride material to saidenvironment containing oxygen ions includes the steps of:exposing saidlayer of tantalum nitride material to a gas containing oxygen; andgenerating a plasma.
 22. The method of claim 21, wherein said plasma isgenerated for approximately 20 seconds.
 23. The method of claim 22,wherein said step of generating said plasma includes the stepsof:providing a first rf signal to a first electrode on a first side ofsaid wafer; and providing a second rf signal to a second electrode on asecond side of said wafer.
 24. The method of claim 23, wherein saidfirst rf signal is substantially 180 degrees out of phase with saidsecond rf signal.
 25. The method of claim 1, further including the stepof:(c) exposing said layer of tantalum nitride material to a gascontaining silicon; and (d) heating said layer of tantalum nitridematerial to cause said silicon to react with said layer of tantalumnitride material.
 26. The method of claim 25, wherein said step (c) andsaid step (d) are performed following said step (b).
 27. The method ofclaim 25, wherein said step (c) and said step (d) are performedfollowing said step (a) and prior to said step (b).
 28. The method ofclaim 25, wherein said gas containing silicon is silane.
 29. The methodof claim 25, further including the step of:(e) repeating said step (a),said step (b), said step (c), and said step (d).
 30. The method of claim25, further including the steps of:(e) depositing a cap layer of saidtantalum nitride material on said layer of tantalum nitride materialfollowing all of said steps (a), (b), (c) and (d); and (f) annealingsaid cap layer of said tantalum nitride material.
 31. The method ofclaim 25, wherein said step (a), said step (b), said step (c), and saidstep (d) are all performed in a chamber without removing the wafer fromthe chamber between initiating said step (a) and completing said step(d).
 32. The method of claim 25, wherein said layer of tantalum nitridematerial is deposited using chemical vapor deposition.
 33. The method ofclaim 25, wherein said step (a), said step (b), said step (c) and saidstep (d) are all performed in a chamber without removing the wafer fromthe chamber between initiating said step (a) and completing said step(d).
 34. A method for constructing a diffusion barrier on a wafer, saidmethod comprising the steps of:(a) placing said wafer in a processingchamber; (b) depositing a layer of tantalum nitride material on saidwafer, while said wafer is in said processing chamber; and (c) followingsaid step (b), plasma annealing said deposited layer of tantalum nitridematerial, while said wafer is in said processing chamber.
 35. The methodof claim 33, wherein said step (c) includes the steps of:exposing saidlayer of tantalum nitride material to an environment containing ions.36. The method of claim 34, wherein said step (c) includes the stepsof:electrically biasing said layer of tantalum nitride material to causesaid ions from said environment to impact said layer of tantalum nitridematerial.
 37. The method of claim 34, wherein said step of exposing saidlayer of tantalum nitride material to said environment containing ionsincludes the steps of:providing a gas; and providing energy to said gas.38. The method of claim 36 wherein said energy is provided by an RFsource having an output power of greater than approximately 350 watts.39. The method of claim 36 wherein said energy is provided by an RFsource having an output power of approximately 900 watts.
 40. The methodof claim 33, wherein said step (b) is performed using thermal chemicalvapor deposition.
 41. A method for constructing a tantalum nitride filmon a semiconductor wafer, said method comprising:(a) depositing a layerof tantalum nitride material on said wafer using thermal chemical vapordeposition; and (b) following said step (a), plasma annealing said layerof tantalum nitride material, where plasma for the plasma annealing stepis formed by applying a RF signal having a power greater than 350 wattsto hydrogen gas.